Performance Study of a Chain–Spoon Seed Potato Discharger Based on DEM-MBD Coupling

Abstract

To address the issues of the poor filling and clearing efficiency of spoon–chain potato seed dischargers, an optimization design was implemented in this study. Based on the motion characteristics of potatoes during the filling and transport processes, an inclination angle was set for the seed spoon cavity, and a seed-clearing brush was installed at the top of the seed discharger. A DEM-MBD coupled simulation model of the seed discharger was constructed. The working speed of the driving sprocket, the inclination angle of the seed spoon cavity, and the seed holding height were used as experimental factors, while the single-seed qualification rate, missed seed rate, and over-seeding rate were used as evaluation indices to conduct a quadratic regression orthogonal rotation combination experiment. This determined the optimal technical parameter combination for the best working performance. Based on the results of the DEM-MBD coupled simulation experiments, a response surface optimization test was conducted. The results showed that the optimal working performance was achieved when the working speed of the driving sprocket was 43 rpm, the inclination angle of the seed spoon cavity was 15°, and the seed holding height was 0.2 m. Under these conditions, the single-seed qualification rate was 95.28%, the missed seed rate was 0.92%, and the over-seeding rate was 3.80%. Further soil bin tests confirmed that, under the optimal working parameters, the relative deviations of all test indices from the response surface optimization test results were less than 2%. The research results provide new insights for the optimization design of spoon–chain potato seed-metering devices.

1. Introduction

Potatoes, as one of the world’s most important food crops, have seen a steady increase in both planting area and yield [1]. The mechanization level of potato planting is particularly crucial for the design and optimization of seed discharger [2]. Chain-type seed potato dischargers face issues such as poor seed clearing and the inability to effectively remove excess seeds from the spoons, resulting in severe seed missing and double seeding phenomena that negatively impact the overall seeding efficiency [3]. Therefore, enhancing the seeding and seed clearing performance of chain-type potato seeders is a pressing technical challenge.

The VL19E dual-row potato planter, developed by the German company GRIMME, comprises a frame, spoon-type seed discharger, furrow opener, soil covering and ridging discs, rubber pneumatic ground wheels, a chain transmission mechanism, and a hopper. The field trials conducted by Liu Jiping and others on the equipment showed that this machine features stable transmission, a compact structure, reliable and uniform seeding, and high operational quality, but there is still the issue of a relatively high missed seed rate [4]. Gulati et al. [5] designed a spoon–chain potato planter that, despite being manually driven, picks up seeds and drops them through the rotation of the seed discharge chain driven by the ground wheel, exhibited good seeding uniformity and low production costs but high labor consumption, and it is not suitable for large-area planting. Buitenwerf et al. [6] analyzed and tested the motion state of a spoon-type seed discharger using mathematical modeling, identifying the seed delivery tube and seed uniformity as significant influencing factors. In 2007, the European Union organized the design of a chain seed discharger using a horizontal chain conveyor mechanism to transport seed potato laterally into the furrow, significantly reducing the missed seed rate [7].

In the late 1950s, China began researching precision potato seeding, with spoon–chain seed-metering technology being widely applied. With the advancement of society and technology, potato planters in China have been continually improved and optimized [8]. Zhao Manquan et al. [9] developed a potato ridge planter with a spoon–chain seed discharger, which includes a furrow opener and fertilizer applicator, capable of completing furrowing, fertilizing, seeding, soil covering, and compaction in one operation. Zhao Manquan et al. optimized parameters such as the soil entry angle, clearance angle, and skew angle of the seeder, and they also optimized the design of the seed discharge chain and the chain and spoon of the seed discharger to achieve adjustable plant spacing. The overall performance of the machine is reliable, but there are still issues such as severe over-seeding and a relatively high seed volume. Zhou Guixia et al. [10] designed the 2CM-2 potato planter, which consists of a furrow opener, ground wheel, fertilizing and seeding device, soil covering plow, and frame, using a hook-type chain–spoon seed discharge mechanism. Spoons on adjacent hook-shaped chains are arranged in a staggered configuration, achieving staggered planting within rows and between rows. To accommodate different sizes of potato tubers, corresponding-sized plastic seed cups are attached to the universal spoons. For tubers with diameters less than 30 mm, plastic seed cups can be fitted inside the original cups, improving the seeding accuracy to some extent and enabling staggered planting within a single row. However, since this model of seed planter does not have a seed-clearing mechanism, it still has the issue of a relatively high over-seeding rate. Lü Jinqing et al. [11], from Northeast Agricultural University, developed a spoon-type seed discharger suitable for both large and small tubers, addressing the common issues of missed seeding and over-seeding and high labor consumption. This device comprises a seeding belt, a seed-clearing device, spoons, an anti-jamming ejector rod, and a frame, with the spoons arranged in a staggered double-row pattern. To improve the versatility of the seed spoon, a 20 mm diameter round hole is machined at the bottom of the spoon to accommodate miniaturized seed cups. Additionally, the seed discharger includes a seed-clearing system, which consists of a vibrating seed-clearing device and an anti-jamming rod. A cam wheel is installed behind the seed-dispensing belt in the seed-clearing area. The cam wheel serves as the vibration source and presses against the seed-dispensing belt. A DC motor drives the cam wheel, causing the belt to vibrate perpendicularly to its direction. Excess tubers in the spoons fall off due to the vibration, achieving primary seed clearing. The anti-jamming rod is installed at the top of the seed-dispensing belt, between two seed spoons, with a protruding length of 280 mm, which is greater than the diameter of the drive wheel. When tubers are jammed between spoons, the anti-jamming rod prevents them from moving upward, causing them to fall back into the seed hopper, achieving secondary seed clearing. Bench tests were conducted to determine the main influencing factors and optimal parameters of the seeding performance, verifying the seeding performance under optimal parameters. This provides solutions to common problems with potato dischargers, including high rates of over-seeding, high rates of missed seeding, and poor versatility.

In recent years, with the continuous development of agricultural mechanization technology, the application of DEM-MBD coupled simulation technology has provided new approaches and methods for the design and optimization of seed-metering devices [12]. Researchers at Kunming University of Science and Technology, led by Lai Qinghui, conducted a study on a precision chain–spoon ginseng seed discharger based on the coupling of DEM and MBD [13]. They analyzed the effects of different tensions in the seed-dispensing chain, various structural parameters, and operational parameters on the performance of the seed discharger, determining the structural parameters of the chain–spoon seed discharger. At Huazhong Agricultural University, Tan Benfang and colleagues carried out performance simulation studies on a triangular chain–cup–spoon potato discharger based on the coupling of RecurDyn and EDEM [14]. They constructed a coupled simulation model using RecurDyn and EDEM and separately analyzed the seed filling stage and the seed clearing stage. They established multiple regression models for the over-seeding index, the missed-seeding index, working speed, seed filling angle, and seed layer height, and they obtained the optimal parameter combination through multi-objective optimization methods. This study aims to optimize the design of a chain–spoon seed potato discharger by adjusting the inclination angle of the inner cavity of the seed spoons and adding a seed-clearing brush, thereby improving the seeding and seed clearing performance of the seeders. Based on DEM-MBD coupled simulation experiments, a systematic analysis of the working parameters of the key components on the performance of the seed discharger was conducted to determine the optimal parameter combination, and bench tests were used to verify its performance. The research results provide theoretical and technical support for the optimal design of chain–spoon seed potato dischargers, significantly contributing to the mechanization level of potato planting.

2. Materials and Methods

2.1. Overall Structure and Working Principle

The working mode of the chain–spoon seed potato discharger in this study is a single-unit, double-row type, as shown in Figure 1. The seed discharger primarily consists of an auxiliary seed box, seed discharge box, seed protection groove, seed spoon, seed discharge sprocket, seed discharge chain, seed-clearing brush, and vibrating screen wheel.

As shown in Figure 2, during the initial seed filling phase, the drive sprocket drives the seed discharge chain, causing the seed spoons to sequentially enter the seed filling area. These spoons penetrate the seed layer and carry the seed potatoes upwards. Due to the inclination angle of the seed spoon cavity, excess seed potatoes outside the cavity fall back into the seed box under the influence of gravity. Concurrently, the rubber plate at the bottom of the seed box oscillates up and down due to the action of the vibrating screen wheel, enhancing the flow of seed potatoes within the seed box and improving the seed filling performance.

When the seed spoons carrying the seed potatoes move to the clearing area, any excess seed potatoes that have not fallen off during the transport are dislodged by the seed-clearing brush and fall back into the seed box. After crossing the drive sprocket, the seed potatoes drop into the bottom cavity of the preceding seed spoon, entering the seeding zone. As the seed spoon moves to the seeding point, the seed potatoes fall freely into the seed furrow, completing the entire seeding process.

2.2. Key Component Structural Optimization Design

2.2.1. Optimization Design of Seed Spoon

The seed spoon is the core component of the seed discharger, and its structural design directly affects the performance of the discharger [15]. To reduce the rate of seed duplication, the seed spoon cavity is designed with a certain inclination angle, which assists in clearing excess seeds during seed transport. Additionally, a concave cavity is placed at the bottom of the seed spoon, allowing seed potatoes to fall into the rear cavity of the spoon when entering the seeding zone. This design minimizes continuous random friction and collisions between the seed potatoes, the seed protection groove, and the chain during the seeding phase, thereby reducing seed potato damage. It also helps to maintain a relatively fixed seeding position, improving the uniformity of plant spacing during the operation of the seed discharger.

The main structural parameters of the seed spoon include the inclination angle θ, the height A, the upper cavity opening diameter D, the bottom cavity opening diameter B, the upper cavity depth H, the bottom cavity depth h, and the concave cross-sectional curve of the upper cavity, as shown in Figure 3.

The structural parameters of the seed spoon are related to the overall dimensions of the seed potatoes. The design should follow the principle D > $\overline{L}$ > $\overline{W}$ > 2H [16], where D is the upper cavity opening diameter, $\overline{L}$ is the average length of the seed potatoes, $\overline{W}$ is the average width of the seed potatoes, and H is the upper cavity depth.

For potato planting operations, cut seed potatoes are generally used [17]. According to the relevant literature, the average mass of a cut seed potato is around 50 g, with a density of between 1000 and 1200 kg/m³. Thus, the equivalent diameter of a cut seed potato ranges from 34.2 to 36.2 mm [18]. Considering the significant variability in the shape of cut seed potatoes, D is set to 40 mm and the upper cavity depth to 18 mm. To ensure that the seed potato can smoothly fall into the lower cavity of the preceding seed spoon during the throwing process, the lower cavity opening diameter B should be slightly larger than the upper cavity opening diameter D. Therefore, B is set to 45 mm, the lower cavity depth to 10 mm, and the seed spoon height A to 38 mm.

• Inclination Angle of the Seed Spoon Cavity

The inclination angle of the seed spoon cavity is defined as the angle between the normal to the direction of seed spoon movement and the bottom plane of the seed spoon cavity. Setting this inclination angle assists in the removal of excess seeds during the seed transport process.

This analysis focuses on the moment when the seed spoon has fully penetrated the seed layer. At this point, the seed potatoes outside the cavity that are carried by the seed spoon are analyzed for their kinematic and static behaviors, as shown in Figure 4.

The kinematic analysis shows that the tangential acceleration a_e of the seed potatoes outside the seed spoon cavity is aligned with the direction of the seed spoon’s movement. The direction of the relative acceleration a_r is related to the inclination angle of the seed spoon cavity. When the absolute acceleration a_e of the seed potatoes outside the seed spoon cavity falls within the first quadrant of the coordinate system, the seed spoon demonstrates a certain degree of seed clearing capability [13].

The static analysis of the seed potatoes outside the seed spoon cavity should satisfy the following conditions:

$$\left\{\begin{array}{c}{a}_r>0\\ \theta <{\phi }_{abs}\end{array}\right.$$

(1)

$$\left\{\begin{array}{c}{F}_N=mg\cos \theta \\ F_S=F_N{\mu }_S\\ m{a}_r=mg\sin \theta -F_S\end{array}\right.$$

(2)

From Equations (1) and (2), we can obtain:

$$\theta >{\tan }^{-1}{\mu }_S$$

(3)

where θ is the inclination angle of the seed spoon cavity, °; φ_abs is the maximum friction angle between the seed potatoes and the seed spoon; F_N is the normal force exerted on the seed potatoes outside the seed spoon cavity, N; F_S is the frictional force exerted on the seed potatoes outside the seed spoon cavity, N; ${\mu }_S$ is the coefficient of kinetic friction between the seed potatoes; m is the mass of the seed potatoes, kg; and g is the gravitational acceleration, m/s². The maximum friction angle between the seed potatoes and the seed spoon is ${\phi }_{abs}$ = 16.75° (with the seed spoon material being ABS plastic), and the coefficient of kinetic friction between the seed potatoes is ${\mu }_S$ = 0.110 [19]. Therefore, the range for the inclination angle of the seed spoon cavity is determined to be 6.85° to 16.75°.

2.2.2. Driving Sprocket

To ensure that the seed potatoes are not thrown out when crossing over the drive sprocket, a static analysis of the seed potatoes’ motion at this stage is conducted in this section [20]. As shown in Figure 5, the seed potatoes are in a critical state, about to enter the seeding zone. At this point, the seed potatoes are affected by the centrifugal force Fc from the drive sprocket, the frictional force Fs from the seed spoon, the supporting force F_N from the seed spoon, and their own weight G.

If the resultant force of the frictional force and weight is less than the centrifugal force, the seed potatoes will be thrown out. To ensure that the seed potatoes successfully enter the seeding zone, the following force balance conditions must be satisfied:

$$\left\{\begin{array}{l}{F}_s\cos {\theta }_1+G\mathrm{s}\mathrm{i}\mathrm{n}{\theta }_2\ge F_c\\ F_N\cos {\theta }_1=G\mathit{cos}{\theta }_2\\ F_s=F_N\mu \\ F_c=m{\displaystyle \frac{v^2}{R}}\end{array}\right.$$

(4)

where $\mu$ is the coefficient of friction between the seed potatoes and the seed spoon; ${\theta }_1$ is the inclination angle of the seed spoon cavity, °; ${\theta }_2$ is the relative rotation angle of the seed spoon, °; v is the linear velocity of the drive sprocket, m/s; and R is the radius of the drive sprocket, mm.

By rearranging Equation (4), we obtain the following:

$$R\ge {\displaystyle \frac{v^2}{g(\mathit{sin}{\theta }_2+\mu \mathit{cos}{\theta }_2)}}$$

(5)

$$n\le \sqrt{{\displaystyle \frac{g\left(\sin {\theta }_2+\mu \cos {\theta }_2\right)}{4{\pi }^{2}R}}}$$

(6)

where n is the drive sprocket speed.

According to the relevant literature, when the linear velocity of the drive sprocket is 0.5 m/s, the performance of the seed discharger is optimal. If the linear velocity exceeds 0.5 m/s, the performance significantly declines, leading to severe seed leakage issues [18]. Therefore, the linear velocity v of the drive sprocket is set as 0.5 m/s, gravitational acceleration g is 9.8 m/s², and the coefficient of friction μ is set as 0.42 [14]. The relative rotation angle of the seed spoon is chosen to be between 40 and 100°, and the range for the inclination angle of the seed spoon cavity is set to range from 6.85 to 16.75°. By substituting these parameters into Equations (5) and (6), it is determined that the drive sprocket radius R should be at least 0.064 m. Considering this, a drive sprocket radius R of 80 mm is selected. Consequently, the rotational speed of the drive sprocket should be less than 54.2 rpm.

2.2.3. Seed-Clearing Brush

The seed-clearing brush designed in this study is shown in Figure 6. The brush is installed above the seed protection groove, and power is transmitted to the brush shaft via a chain drive from the drive sprocket. When the seed spoon, carrying multiple seed potatoes, reaches the seed clearing area, as illustrated in Figure 6, the excess seed potatoes outside the seed spoon cavity fall off due to their own gravity and the inertial force generated by the rotating clearing brush and return to the seed box [21].

To ensure that the seed-clearing brush has good clearing performance, the linear velocity v of the clearing brush should be greater than or equal to the linear velocity v of the seed discharge chain. Preliminary experiments have shown that with a transmission ratio of approximately 1.5, where the drive sprocket and driven sprocket have 17 and 25 teeth, respectively, the clearing brush operates relatively stably during the clearing process, and the seed potatoes are less likely to be damaged [21].

According to the sprocket transmission relationship, the following can be obtained:

$$n_s=n_1{\displaystyle \frac{z_1}{z_2}}$$

(7)

$$v_s={\displaystyle \frac{\pi d_s{n}_s}{60\times 1000}}$$

(8)

where n₁ is the rotational speed of the drive sprocket, rpm; z₁ is the number of teeth on the drive sprocket; z₂ is the number of teeth on the driven sprocket; n_s is the rotational speed of the clearing brush roller, rpm; d_s is the diameter of the clearing brush roller, mm; and v_s is the linear velocity of the clearing brush roller, m/s.

Since the linear velocity v_s of the clearing brush roller should be greater than or equal to the linear velocity v of the seed discharge chain, v_s ≥ v, and the previously determined maximum rotational speed of the drive sprocket is 54.2 rpm, with the seed spoon’s working speed not exceeding 0.5 m/s, and the diameter of the clearing brush roller d_s must be at least 119.82 mm. The radius of the clearing brush roller cannot exceed the center distance between the drive sprocket and the driven sprocket; thus, 119.82 mm ≤ d_s ≤ 187.4. The specific structural parameters will be further determined through the analysis of the clearing process.

Using seed potatoes as the study object, the relationship between various factors and the clearing performance is examined in this section. As shown in Figure 7, seed potato 2 remains in an unstable state due to its own weight G and the supporting forces from seed potato 1 and the seed spoon wall. When the seed spoon carrying the seed potatoes is about to cross the drive sprocket, seed potato 2 is subjected to the inertial force F_N2 caused by the rotation of the clearing brush, causing it to fall from the seed spoon and return to the seed box.

During the seed clearing process, seed potato 2 is subjected to the supporting forces N₁, F_N2, and F_N3 from seed potato 1, the clearing brush, and the seed spoon, respectively. Additionally, it experiences frictional forces N_f1, F_f2, and F_f3 from seed potato 1, the clearing brush, and the seed spoon, respectively, as well as its own weight G. As shown in Figure 7, the equation is as follows:

$$\left\{\begin{array}{l}{N}_{f1}=N_1{\mu }_{N1}\\ F_{f2}=F_{N2}\mu \\ F_{f3}=F_{N3}\mu \end{array}\right.$$

(9)

In the equation, μ_N1 and μ represent the friction coefficients.

The net force in the Y-axis acting on seed potato 2 is given by Equation (10):

$$F_y=N_1\sin {\theta }_2+F_{f2}\sin {\theta }_1+F_{N3}\sin {\theta }_3+F_{f3}\cos {\theta }_3-N_{f1}\cos {\theta }_2-F_{N2}\cos {\theta }_1-G$$

(10)

Substituting Equation (9) into Equation (10) yields Equation (11):

$$F_y=N_1\left(\sin {\theta }_2-f_{N1}\cos {\theta }_2\right)+F_{N2}\left(f\sin {\theta }_1-\cos {\theta }_1\right)+F_{N3}\left(\sin {\theta }_3+f\cos {\theta }_3\right)-G$$

(11)

The condition for a seed potato to be removed by the brush is that the net force in the positive Y-axis direction must be greater than zero, as given by Equation (12):

$$N_1\left(\sin {\theta }_2-f_{N1}\cos {\theta }_2\right)+F_{N2}\left(f\sin {\theta }_1-\cos {\theta }_1\right)+F_{N3}\left(\sin {\theta }_3+f\cos {\theta }_3\right)-G>0$$

(12)

The force exerted by the clearing brush on the seed potatoes is related to the clearing distance s. As the clearing distance s increases, the force exerted on the seed potatoes decreases, resulting in poorer clearing effectiveness. Conversely, a smaller clearing distance s increases the contact area between the brush and the seed potatoes, which may lead to damage. Therefore, the clearing distance s is a crucial factor affecting the clearing performance. When designing the clearing distance s, the length of the brush bristles must also be considered. Shorter bristles result in a stiffer brush, while longer bristles make the brush softer. The stiffness of the brush directly impacts the clearing effectiveness and can cause damage to the seed potatoes if the brush is too stiff. In this device, a clearing brush with nylon bristles with a 0.2 mm diameter and a bristle length greater than 8 mm is used. This type of brush roller enhances the adaptability of the seed discharger to different sizes of seed potatoes and causes minimal damage. The equivalent diameter of cut seed potatoes ranges from 34.2 to 36.2 mm, and the center distance between the drive and driven sprockets is 187.4 mm. As shown in Figure 7, when the seed spoon begins to enter the clearing area, the maximum contact distance with the clearing brush is established. To ensure safe contact between the brush roller and the seed potatoes (without causing damage), five sizes of brush rollers were designed based on the overall structure of the seed discharger. The bristle lengths of these rollers are 25, 30, 35, 40, and 45 mm, with corresponding outer diameters of 120, 130, 140, 150, and 160 mm. The corresponding clearing distances are 20, 25, 30, 35 and 40 mm, respectively. Subsequent experiments were conducted to explore the optimal clearing distance.

2.3. Design and Testing Based on DEM-MBD Coupled Simulation

In the operation of the chain–spoon seed potato discharger, the seed potatoes are influenced by the interaction forces between the seeds, which require analysis using the discrete element method (DEM). The movement of the seed discharge chain needs to be analyzed using multibody dynamics (MBD). Therefore, a coupled simulation method combining DEM and MBD was used for the analysis [22]. The simulation analysis process using the coupling of RecurDyn and EDEM is shown in Figure 8.

2.3.1. Establishment of Simulation Model

• Multibody Dynamics 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.

• Discrete Element Model

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. Discrete element simulation parameters.

Parameter	Seed Potato	65 Mn Steel	ABS Plastic
Poisson’s Ratio	0.57	0.30	0.34
Shear Modulus (Pa)	1.34 × 106	7.0 × 1010	3.0 × 109
Density (kg/m3)	1.048 × 103	7.8 × 103	1.25 × 103
Coefficient of Restitution with Seed Potatoes	0.79	0.71	0.66
Static Friction Coefficient with Seed Potatoes	0.452	0.445	0.517
Rolling Friction Coefficient with Seed Potatoes	0.024	0.269	0.303

[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.

• Impact of Different Drive Sprocket Operating Speeds on Seed Filling Performance

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. Effect of drive sprocket operating speed on seed filling performance.

Operating Speed (rpm)	Single-Seed Qualification Rate/%	Missed Seed Rate/%	Over-Seeding Rate/%
14.0	64.45	5.42	30.13
24.0	75.67	5.61	18.72
34.0	77.20	8.93	13.87
44.0	77.58	9.93	12.49
54.0	81.88	14.10	4.02

.

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.

• Impact of Different Seed Scoop Cavity Angles on Seed Filling Performance

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. Effect of seed scoop cavity angle on seed filling performance.

Seed Scoop Cavity Angle (°)	Single-Seed Qualification Rate/%	Missed Seed Rate/%	Over-Seeding Rate/%
7.0	61.66	5.08	33.26
9.5	62.95	5.24	31.81
12.0	67.27	7.63	25.10
14.5	69.63	8.17	22.20
17.0	63.64	21.89	14.47

.

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°.

• Impact of Different Seed Capacity Heights on Seed Filling Performance

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. Effect of seed capacity height on seed filling performance.

Seed Capacity Height (m)	Single-Seed Qualification Rate (%)	Missed Seed Rate (%)	Over-Seeding Rate (%)
0.12	51.90	42.68	5.42
0.16	61.43	28.43	10.14
0.20	76.86	9.01	14.13
0.24	73.23	8.75	18.02
0.28	59.55	7.91	32.54

.

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.

• Effect of Different Clearing Distances on Clearing Performance

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. Effect of seed clearing distance on seed clearing performance.

Clearing Distance (mm)	Single-Seed Qualification Rate/%	Missed Seed Rate/%	Over-Seeding Rate/%
20	70.16	13.61	16.23
25	76.21	9.64	14.15
30	83.57	6.04	10.39
35	70.19	22.96	6.85
40	66.52	30.68	2.8

.

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.

• Effect of Different Clearing Brush Rotational Speeds on Clearing Performance

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. Effect of seed-clearing brush speed on seed clearing performance.

Seed-Clearing Brush Rotational Speed (rpm)	Single-Seed Qualification Rate/%	Missed Seed Rate/%	Over-Seeding Rate/%
51.0	81.64	2.18	16.18
58.5	87.56	2.19	10.25
66.0	94.21	1.07	4.72
73.5	70.06	27.84	2.10
81.0	57.25	41.84	0.91

.

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.

3. Results

3.1. Results of Response Surface Test

The previous analysis covered the seed filling and clearing processes of the seed discharger and determined the parameter ranges for the active chain wheel speed, seed scoop cavity angle, and seed scoop capacity height through single-factor simulation tests. To find the optimal working parameter combination, an orthogonal test was conducted. The test used the single-seed qualification rate Y₁, miss rate Y₂, and re-seeding rate Y₃ to evaluate the results. The test scheme and results are shown in

Table 7. Experimental factors and levels.

Level	Experimental Factors
	Operating Speed X1 (rpm)	Seed Scoop Cavity Angle X2 (°)	Seed Capacity Height X3 (m)
−1.682	34	12.0	0.16
−1	39	13.25	0.18
0	44	14.5	0.20
1	49	15.75	0.22
+1.682	54	17.0	0.24

.

In the secondary regression orthogonal combination test, each group of tests was conducted three times, and the average value was used as the test result data. The results were then entered into the test scheme and results table, as shown in

Table 8. Experimental design and results.

Level	Experimental Factors			Experimental Indicators
	Operating Speed X1 (rpm)	Seed Scoop Cavity Angle X2 (°)	Seed Capacity Height X3 (m)	Single-Seed Qualification Rate (%)	Missed Seed Rate (%)	Over-Seeding Rate (%)
1	39	13.25	0.18	92.16	3.68	4.16
2	49	13.25	0.18	88.19	3.74	8.07
3	39	15.75	0.18	93.43	2.52	4.05
4	49	15.75	0.18	92.65	2.77	4.58
5	39	13.25	0.22	86.72	1.06	12.22
6	49	13.25	0.22	89.91	1.42	8.67
7	39	15.75	0.22	87.98	1.68	10.34
8	49	15.75	0.22	91.96	4.02	4.02
9	34	14.5	0.20	88.84	1.79	9.37
10	54	14.5	0.20	90.01	3.96	6.03
11	44	12.0	0.20	85.48	0.96	13.56
12	44	17.0	0.20	93.17	2.94	3.89
13	44	14.5	0.16	92.5	4.57	2.93
14	44	14.5	0.24	87.12	0.91	11.97
15	44	14.5	0.20	94.66	1.02	4.32
16	44	14.5	0.20	94.71	1.39	3.9
17	44	14.5	0.20	96.5	0.97	2.53
18	44	14.5	0.20	96.68	0.97	2.35
19	44	14.5	0.20	95.05	0.1	4.85
20	44	14.5	0.20	94.38	1.38	4.24

.

Using the Design-expert 13 software, the test results were subjected to multiple regression fitting to obtain mathematical regression models relating the test indicators to the experimental factors. This study only conducted variance analysis for the single-seed qualification rate and the missed seed rate of the chain scoop potato planter. The variance analysis results are shown in

Table 9. Analysis of variance for single-seed qualification rate and missed seed rate.

Source of Variation	Single-Seed Qualification Rate				Missed Seed Rate
	Sum of Squares	Degrees of Freedom	F	p	Sum of Squares	Degrees of Freedom	F	p
Model	200.46	9	14.59	0.0001 **	29.71	9	9.93	0.0006 **
X1	1.41	1	0.9235	0.3592	3.25	1	9.77	0.0108 *
X2	35.35	1	23.16	0.0007 **	1.43	1	4.30	0.0648
X3	26.18	1	17.15	0.0020 **	8.36	1	25.15	0.0005 **
X1X2	1.98	1	1.30	0.2813	0.5886	1	1.77	0.2129
X1X3	17.76	1	11.63	0.0066 **	0.7140	1	2.15	0.1735
X2X3	0.7320	1	0.4796	0.5044	3.58	1	10.76	0.0083 **
X12	48.42	1	31.72	0.0002 **	6.51	1	19.57	0.0013 **
X22	50.30	1	32.95	0.0002 **	1.71	1	5.16	0.0465 *
X32	41.49	1	27.18	0.0004 **	5.62	1	16.89	0.0021 **
Residual	15.26	10			3.32	10
Lack of Fit	10.26	5	2.05	0.2248	2.22	5	2.01	0.2306
Error	5.01	5			1.10	5
Total	215.73	19			33.04	19

** means extremely significant (p < 0.01); * means significant (0.01 < p < 0.05).

. The regression equations for the single-seed qualification rate Y₁ and the missed seed rate Y₂ were highly significant (p < 0.01), and the regression equation’s lack-of-fit terms were not significant p > 0.05). By removing the insignificant influencing factors, the regression equations for the single-seed qualification rate Y₁ and the missed seed rate Y₂ with respect to the working speed of the main wheel X₁ and the capacity height X₂ were obtained as follows:

Y₁ = 95.30 + 1.61X₂ − 1.39X₃ + 1.49X₁X₃ − 1.83X₁² − 1.87X₂² − 1.70X₃²

(13)

Y₂ = 0.97 + 0.49X₁ + 0.32X₂ − 0.78X₃ + 0.66X₂X₃ + 0.67X₁² + 0.34X₂² + 0.62X₃²

(14)

From Table 9, it can be seen that the primary and secondary factors affecting the single-seed qualification rate were the seed scoop cavity angle, seed capacity height, and operating speed. The interaction between the main wheel speed and container height should not be ignored, as shown in the response surface in Figure 21. For the missed seed rate, the primary and secondary factors were the container height, main wheel speed, and scoop cavity inclination. The interaction between the container height and scoop cavity inclination should not be overlooked, as illustrated in the response surface in Figure 21.

3.2. Optimization of Experimental Results

To optimize the best combination of the experimental factors, a parametric mathematical model was established. The single-seed qualification rate and missed seed rate were used as the evaluation indicators. The regression equations for these indicators were analyzed to obtain a nonlinear programming mathematical model. A multi-objective optimization of the evaluation indicators’ regression model was performed with the objective function and constraints as follows:

$$\left\{\begin{array}{c}max{Y}_1(X_1,X_2,X_3)\\ min{Y}_2(X_1,X_2,X_3)\\ 34\le X_1\le 54\\ 12.0\le X_2\le 17.0\\ 0.16\le X_3\le 0.24\end{array}\right.$$

(15)

Considering the convenience of manufacturing the planter, integer values were selected for all the parameters. The optimal working parameters for the planter were determined to be a driving wheel speed of 43 rpm (with a seed-clearing brush speed of 64.5 rpm), a seed scoop cavity angle of 15°, and a seed height of 0.2 m. At these settings, the seeding phase achieved a single-seed qualification rate of 95.28%, a missed seed rate of 0.92%, and an over-seeding index of 3.80%.

3.3. Soil Bin Test Verification

Soil bin tests were conducted at the Mechanical Training Center of Gansu Agricultural University. Before conducting the experiments, the potatoes were cut into pieces. The primary testing equipment included the 2CM-2-type potato planter and the TCC-3-type soil bin vehicle, as shown in Figure 22.

In the previous sections, the optimal working parameters for the seeder were determined through DEM-MBD coupling simulations and the subsequent optimization of the test results. During the soil bin tests, the seeder was set to the parameters obtained from the simulation as follows: a driving wheel speed of 43 rpm, a seed scoop with a cavity angle of 15°, and a seed capacity height of 0.2 m in the seeding box. A comparison of the simulation and soil test results is shown in

Table 10. Comparison of simulation test and soil bin test results.

	Single-Seed Qualification Rate (%)	Missed Seed Rate (%)	Over-Seeding Rate (%)
Simulation Test	95.28	0.92	3.80
Soil Bin Test	94.50	1.26	4.24

.

In the soil bin tests, due to uncontrollable factors such as machine vibrations, there was some deviation from the simulation results. However, the error was within an acceptable range, indicating that the optimal parameter combination determined from the DEM-MBD simulation tests has practical significance for optimizing chain–spoon-type potato seeders.

4. Conclusions

This study optimized the operating parameters of a seed-potato-metering device using the response surface methodology to enhance the single-seed qualification rate and reduce the missed seed rate. During the experiments, we investigated the effects of three factors on the performance of the seed discharger: the driving sprocket speed, the inclination angle of the seed spoon cavity, and the seed capacity height. Based on the experimental results, a series of analyses and optimizations were performed. Simulation experiments using DEM-MBD coupling revealed that during the operation of the seed-potato-metering device, some seed spoons captured two or more seeds after breaking through the seed layer. Traditional seed potato dischargers often face issues with poor seed clearing due to their single clearing method. In this study, the seed spoon cavity was given a certain inclination angle to assist in clearing the seeds during their movement. The simulation results showed that when the inclination angle of the seed spoon cavity was set to 15°, the clearing effect was optimal. Additionally, a seed-clearing brush was installed above the seed protection slot to disturb the seeds just before they passed over the driving sprocket. The simulation experiments indicated that the optimal clearing effect was achieved when the clearing brush speed was 64.5 rpm and the clearing distance was 30 mm. These two methods significantly improved the seed clearing effect of the seed discharger and reduced the rate of multiple seeds being present during the seeding process.

This study designed a chain–spoon-type seed potato discharger, optimized the key components, and conducted single-factor simulation experiments based on DEM-MBD to analyze the effects of the driving sprocket speed, seed spoon cavity inclination angle, and seed capacity height on the seed filling performance of the seed discharger. Through the response surface methodology and optimization of the experimental results, the optimal working parameters of the seed discharger were determined. The optimal parameters were an operating speed of 43 rpm, a seed spoon cavity angle of 15°, and a seed capacity height of 0.2 m. Under these conditions, the seed filling stage achieved a single-seed qualification rate of 95.28%, a missed seed rate of 0.92%, and an over-seeding rate of 3.80%. Verification through soil tank experiments showed that these parameters have practical reference value. Referring to the relevant literature [18], the performance indicators of the seed potato discharger before the optimization were as follows: a single-seed qualification rate of 91%, a missed seed rate of 4%, and an over-seeding rate of 5%. Therefore, the optimization in this article has had a clear effect.

Although this study optimized the working parameters of the seed-metering device to a certain extent, there is still room for further improvement. Future research could focus on the following areas: first, exploring the performance variations under more practical usage environments to further enhance the device’s stability and adaptability; second, considering the inclusion of more operating parameters for optimization to comprehensively improve the performance of the seed-metering device; and third, incorporating intelligent control technology to achieve dynamic adjustments and the real-time optimization of the seed-metering device, thereby improving its overall operational efficiency and quality.

In summary, this study provides a scientific basis for the optimized design of seed dischargers and verified the effectiveness of the optimization results through practical experiments, offering reference for future related research and practical applications.