Numerical Simulation and Test of the Disturbance Air Suction Garlic Seed Metering Device

Abstract

In order to solve the problems of high missed rate and easily damaged seeds in traditional garlic metering devices, an air suction garlic seed metering device was designed. The critical components include a seed tray and a seed disturbing tooth. Seed contour curve fitting and a discrete element method were used to determine the initial parameters. The optimal parameter combinations were obtained through fluid dynamics simulation. With a higher pass seeding rate and a lower missed seeding rate as the goal, the device has been optimized for parameters. The best combination of parameters was obtained: the number of type holes was 9; the diameter of holes was 7.2 mm; the forward speed was 1 km/h; the working negative pressure was −5.5 kPa; the pass seeding rate was 88.54%; and the missed seeding rate was 6.34%. Field trials had shown that the air suction garlic seed metering device designed in this study satisfied the requirements of garlic cultivation. Three tests were conducted and a pass rate of 87.83% and a missed rate of 6.85% were obtained.

1. Introduction

As an important cash crop in China, garlic ranks first in the world in terms of planted area, production and export volume. Garlic cultivation amounted to about 700,000 hectares in 2021, accounting for more than 60% of the global garlic cultivation area [1,2]. In China, the agronomy of garlic cultivation requires small row spacing, high density and single upright sowing. However, there is a low level of mechanization and miniaturization of equipment. Spoon chains, turntables and vibratory seed discharge devices are still widely used [3,4]. For this reason, scholars have made many efforts to improve garlic yield and conformity.

In order to improve the mechanization efficiency of garlic sowing, German scholars developed the Bee-herCG-6 garlic sowing machine, which adopts the seed rower of the eye wheel to achieve the sowing effect of single seed extraction [5]. Bakhtiari, MR et al. [6] designed an innovative tractor-mounted position with ground wheel-driven, triple linkage unit, row crop precision planter capable of planting three rows of garlic on this basis. CHOI et al. [7] designed a garlic planter with a seed transfer scoop pickup and duckbill mechanism for sowing, which can also improve the garlic sowing pass rate in complex fields. With the development of precision sowing technology, scholars have devised more precise technical means to improve the qualification rate of garlic. Zhang et al. [8] designed an electro-hydraulic hybrid regulated garlic planter to achieve matching of plant spacing and operating speed, and was able to detect and display operating parameters and sowing abnormality alarms in real time. Li, T.H. et al. [9] designed a garlic missed seed detection and replanting device with a laser sensor, a rotating spoon seed replacer, and a replanting box, which effectively reduced the missed seeding rate and reseeding rate of garlic. Korea Yongdong Company [10] developed and produced the YD-1500 garlic seeder, which has quite good operation efficiency and operation pass rate. Guo, HP et al. [11] designed a garlic planter with an adjustable size sowing device for efficient single grain metering and sowing of different varieties of garlic.

The pneumatic seed discharger uses the force formed by the vacuum system and atmospheric pressure to realize the grasping and moving of seeds, which is highly adaptable to the shape of seeds. Compared to mechanical seeders, the missed and replay rates are lower, and the injury rate is also reduced. Some experts have conducted in-depth research on air-absorbing seed dispersers and verified that air-absorbing seed dispersers have a higher seeding pass rate. Lü Jinqing [12] designed an air-suction seed discharge device, which achieves high quality seeding by using an air distribution valve fitted with a suction arm. He Xing et al. [13] designed a pneumatic seeder with adjustable seeding volume. According to the requirement of air flow in the seeding discharge device, a sub-pipe and a main pipe were set up, which led to a significant improvement of the seeding pass rate. Zhang Guozhong et al. [14] designed a new precise pneumatic seed metering device with multiple sets of seed suction orifice plates, which can suction 3–4 seeds simultaneously. In terms of garlic, a pneumatic garlic single-grain seed extraction device was developed by Liang et al. [15]. Xie et al. [16] designed a scrambler tooth-assisted pneumatic-suction garlic metering device, which relies on negative pressure to adsorb garlic seed located in the grooves between the scrambler teeth in the seed filling zone, and isolates the negative pressure in the seed feeding zone to separate the garlic seed from the seeding disc to complete a single seeding process. However, these pneumatic seed dispensers are dependent on their own dimensional parameters and can only be advantageous if they are matched to seed size parameters and other factors.

To address the problem of missed seeding in air-suction garlic seeding, this paper uses discrete element simulation [17] and a four-factor, three-level orthogonal test to obtain the optimal combination of parameters for the air-suction seed metering device, which provides a theoretical basis and technical support for the subsequent research of air-suction garlic seeder.

2. Materials and Methods

2.1. Agronomic Requirements and Form Factor Measurement

The selected hybrid garlic from Lai’an, Anhui Province [18] was sown in a finely ground, flat, and without residual tillage stubble, at a depth D of 30~40 mm, and the garlic seeds required for sowing were mainly done by manual splitting. There are two planting patterns for Lai’an hybrid garlic. The first is planted with row spacing R₁ of 270~330 mm and plant spacing P₁ of 65~70 mm. The second is planted with row spacing R₂ of 170 mm and plant spacing P₂ of 100 mm, and the density of both patterns is 30,000 plants/mu to 35,000 plants/mu, with a fertility period of about 240 days. Planting needs to ensure that single seeds are sown, as shown in Figure 1.

The seeds need to be separated from the seed rower as a single grain during sowing, and their morphological dimensions determine the size of the seed extraction structure of the seed rower, which in turn determines the size of the rower as a whole, so the morphological dimensions of the garlic seeds should be measured before the design study of the air suction garlic seed metering device, which can also effectively improve the accuracy and efficiency of the seed metering device [19]. One hundred randomly selected garlic seeds of good quality were used for three axial dimensions measurements, as shown in Figure 2.

The measurement results were analyzed to obtain the frequency distribution of the dimensional intervals in each direction, as shown in Figure 3.

The mean values of the external dimensions of the garlic in Lai’an were measured by vernier calipers in three axes and calculated statistically: the length was 30.7 mm, the width was 15.3 mm and the thickness was 17.4 mm. Equation (1) calculated its equivalent diameter as 20.1 mm, and then its sphericity is 65.5% by Equation (2).

$$D_k=\sqrt[3]{lbh}$$

(1)

where:

• $D_k$—Equivalent diameter of garlic seeds, mm;
• $l$—Average length of garlic seeds, mm;
• $h$—Average width of garlic seeds, mm;
• $b$—Average thickness of garlic seeds, mm.

$$\Phi =\frac{D_k}{L}$$

(2)

By measuring and calculating the sphericity of 65.5%, it can be seen that the size of garlic species is large and the sphericity is low. The low spherical rate implies the complexity of designing a mechanical scoop structure and indicates the unsuitability of the traditional pneumatic seed metering device, which reinforces the importance of creating a unique seed metering device for garlic.

2.2. Theory and Calculation of Model

2.2.1. Seed Discharger Structure Composition and Working Principle

The disturbance air-suction garlic seed metering device [20] designed in this paper mainly consists of a seedbox, an air chamber, and a seed tray, as shown in Figure 4. The seed box and the seed tray have a seed-discharge shaft mounted in the center of the seed box and the seed tray via a bearing. The seed box is equipped with a seed guard, a seed guard brush and a seed-cleaning brush inside, and a negative pressure tube outside the air chamber. The surface of the seed tray has a circumferential distribution of holes and seed-disturbing teeth. During operation, the holes and teeth pass through the seed-filling area, seed-cleaning area, seed-carrying area, and seed-feeding area, as shown in Figure 5. The negative pressure pipe is connected to the negative pressure fan during operation and provides a continuous stable airflow. As the seed-discharge shaft rotates, the seed tray and the seed-disturbing teeth on it also rotate. The garlic seeds piled up in the seed-filling area are bothered by the disturbing teeth. During the movement, the garlic seeds are adsorbed by the negative pressure through the hole, and then the teeth carry the adsorbed garlic seeds into the seed-cleaning area. Some of the extra garlic seeds taken in the cleaning area were returned to the garlic seed population by gravity, and others were brushed off by the cleaning brush and returned to the population, leaving only one garlic seed in the seed-carrying area. Garlic seeds entering the seed-carrying area are still adsorbed on the type pore by negative pressure. When the garlic seeds move to the seed-dropping area, the negative pressure disappears, and the garlic seeds are discharged out of the hole under the action of gravity to complete the seeding work.

2.2.2. Design of Seed Tray

According to the relationship between the filling time of garlic seeds in the seed metering device and the speed of the seed tray, it is known that:

$$\{\begin{array}{c}t=\frac{C_r}{v_p}\\ C_r=\alpha \left(\frac{d_p}{2}-r_k\right)\\ v_p=\frac{\pi n_P}{30}\left(\frac{d_p}{2}-r_k\right)\end{array}$$

(3)

where:

• $t$—Seed filling time, s;
• $C_r$—Length of seed-filling area, m;
• $v_p$—Line speed of seed tray, m/s;
• $\alpha$—Seed-filling angle, rad;
• $d_p$—Diameter of the seed tray, m;
• $n_p$—Rotational speed of seed tray, rpm;
• $r_k$—The radial distance between the center of the hole and the edge of the seed tray, m.

From Equation (3), we get

$$t=\frac{30\alpha }{\pi n_p}$$

(4)

From Equation (4), the diameter of the seed tray does not affect the seed-filling time t. The diameter of the seed tray and the thickness of the seed tray designed in this paper are 300 mm and 5 mm, respectively, considering the characteristics of garlic seed shape, the overall structure size of the seed-metering device, agronomic requirements, and sowing environment requirements.

Equation (5) is the theoretical formula for the number of holes in the seed tray of sphere-like seeds with uniform shape and size. The operating speed of the existing garlic seeder is between 0.36~2 km/h. The rotational speed of the seed-metering device should not be too large for large seeds that are easily broken [21]. The designed matching unit has a forward speed of $v_a$ ≤ 2 km/h and a rotational speed of the seed tray of $n_p$ ≤ 30 rpm.

$$\frac{Z\ast s\ast n_p}{60}=\frac{{\nu }_a}{3.6}$$

(5)

where:

• $v_a$—Unit forward speed, km/h;
• $s$—Seeding spacing, m, garlic agronomy requires plant spacing of 0.08~0.12 m;
• $n_p$—Rotational speed of seed tray, rpm;
• $Z$—The number of teeth and holes.

Because of the shape of garlic seeds, the seed-filling process will be affected by the interaction between garlic seeds. At the same time, the seed-disturbing tooth and hole work in groups. When the number of tooth and hole is large, it is difficult to fill the garlic seed between the two teeth; when the number is small, it leads to a large rotational speed of the seed tray. Therefore, the number of holes needs to be further analyzed. Now, based on the above theoretical analysis, three types of holes are taken, namely 9, 12, and 15 holes, and the following numerical analysis is carried out to select the optimal number of holes through simulation tests, respectively.

The diameter of the hole has a direct effect on the adsorption effect of garlic seeds, and the force analysis diagram is shown in Figure 6.

According to the theory of rigid body dynamics [22], the force equation for a single-grain garlic seed is established as

$$\{\begin{array}{c}{F}_s=P_0·S\\ S=\frac{\pi d^2}{4}\\ \left(F_s-N\right)·\frac{d}{2}=T·B\\ G=mg\\ F_l=m{\omega }^{2}R\\ T=F_l+G+F_f\end{array}$$

(6)

where:

• $G$—Gravity of garlic seed, N;
• $F_l$—Centrifugal force on garlic seed, N;
• $F_f$—Internal frictional resistance between garlic seeds, N;
• $F_s$—Force of hole on garlic seed adsorption, N;
• $N$—The right amount of combined external force on the side, N;
• $T$—The vectorial combined external power of $G$, $F_l$, $F_f$ and $F_r$, N;
• $P_0$—Adsorption pressure through a hole, Pa;
• $m$—Quality of garlic seed, kg;
• $g$—Gravity acceleration, m/s²;
• $\omega$—Angular velocity of the seed tray, rad/s;
• $d$—Diameter of the hole, m;
• $S$—Cross-sectional area of the hole, m²;
• $B$—The distance between the center of gravity of the garlic seed and the seed tray, m;
• $R$—Radius of the circle in which the center of the hole is located, m.

According to Equation (6) above, the adsorption pressure required for a single grain of garlic seed to be adsorbed by the hole instantly is

$$P_0=\frac{4}{\pi d^2}\left(\frac{2TB}{d}+N\right)$$

(7)

When the garlic seed arranger is working in the field, it is not only affected by the interaction between the garlic seeds, but also by the vibration of the seed arranger caused by the field environment. So, it is necessary to consider the seed absorption reliability coefficient $K_1$ = 1.8~2.0, and the external condition coefficient $K_2$ = 1.6~2.0 [23], which can be obtained from Equation (7)

$$P_0=\frac{4K_1{K}_2}{\pi d^2}\left(\frac{2TB}{d}+N\right)$$

(8)

From Equation (8), when $N$ = 0, $P_0$ takes the minimum value, but under the actual working condition, to make the garlic seed adsorbed on the hole, $N$ must be greater than 0. Combining with Equation (7), we can get

$$P_0\ge \frac{8K_1{K}_{2}Bmg}{\pi d^3}\left(1+\lambda +\frac{{\omega }^2}{g}R\right)$$

(9)

where:

• $\lambda$—Combined coefficient of frictional resistance of garlic species.

From Equation (9), the smaller the diameter of the hole on the seeding tray and the greater the speed of the tray, the greater the pressure required for the adsorption of a single hole on the disc.

The diameter of the hole is calculated from Equation (10) [24] according to the triaxial dimensions of the garlic seeds.

$$d_x=ab$$

(10)

where:

• $d_x$—Diameter of a hole, mm;
• $a$—Coefficient, generally taken as 0.64~0.66 [25];
• $b$—Average width of garlic seeds, mm.

The average width of 15.3 mm is substituted into Equation (10), but the garlic seed width is less than the average width of garlic seeds. For this part of the garlic seeds, the diameter of the hole should be smaller than the diameter of the hole calculated from the average width when designing. If the average width is used to calculate the diameter of the pore, this may not be well closed when adsorbing small garlic seeds, so the seeds will fall off or leak. And for the garlic seeds with larger seeds, a better adsorption effect can be achieved by increasing the pressure.

Therefore, the design of the hole diameter to ensure that the pressure is not too large premises a moderate reduction in the diameter of the hole. This paper designs three types of hole diameters, which are 6 mm, 8 mm and 10 mm. In the following section, fluent simulation tests are conducted for the diameters of three holes to take the optimal hole diameter. The numeric selection is shown in

Table 1. Numeric selection.

Name	Numerical Selection
The number of hole and tooth	9, 12, 15
the diameter of the hole (mm)	6, 8, 10

.

2.2.3. Seed-Disturbing Tooth Design

In the design of the structure of the seed-disturbing tooth, the single seed extraction should be satisfied, and the distribution of the seed-disturbing tooth should avoid the occurrence of multiple extractions, miss, blockage, and injury of garlic seeds, etc. In order to improve the contact area between the garlic seeds and the seed-disturbing tooth, the curvature of the seed-disturbing tooth was bent with reference to the curvature of the dorsal arches of Lai’an hybrid garlic. One hundred garlic seeds were randomly selected and cut into two halves from the middle symmetry line of the dorsal arch surface. Then MATLAB was used to binarize the garlic seeds and extract the garlic seed profile [26], and the extraction process is shown in Figure 7.

According to the garlic species back-arch surface profile, a blue parabola is fitted as shown in Figure 8, the vertex of the parabola passes through the origin, another point on the parabola is randomly selected, and a quadratic polynomial is used to obtain the equation of the blue parabola as

$$y=0.038x^2$$

(11)

Because of the large and irregular seeds of garlic seeds, which lead to poor mobility of garlic seeds, the distance between two seed-disturbing teeth should meet the entry of garlic seeds in any attitude in order to avoid the blockage of garlic seeds. The structural parameters of the seed-disturbing teeth are designed as shown in Figure 9.

Figure 9. Schematic diagram of seed-disturbing teeth structure.

Figure 9. Schematic diagram of seed-disturbing teeth structure.

$$\{\begin{array}{c}{l}_s<l<l_s+h_s\\ l_s<l_{ab}\\ h_s\le h\le 2h_s\\ r_2-r_1\le \frac{h}{2}\end{array}$$

(12)

where:

• $l_s$—Average length of garlic seeds, mm;
• $l$—Length of a seed-disturbing tooth, mm;
• $l_{ab}$—Distance between $ab$ at the smallest of two seed-disturbing teeth, mm;
• $h_s$—Average width of garlic seeds, mm;
• $h$—Width of a seed-disturbing tooth, mm;
• $r_2$—Outer circle radius of seed-disturbing tooth, mm;
• $r_1$—Inner circle outer diameter of a seed-disturbing tooth, mm.

According to the average length of the garlic seeds and the equation of the contour of the back arch of the garlic seeds, the length of the seed-disturbing tooth is slightly larger than the average length of the garlic seeds. In this paper, the length of the disturbing tooth is 32 mm, so the arc of the tooth profile can be taken as a parabola in the range of $x\in$ (−16 mm, 16 mm), and the thickness of the tooth is taken as 5 mm. Following this, the left and right sides of the seed-disturbing tooth can be taken as arcs with radii of 45 mm and 50 mm, and the above and below contours consist of arcs with radii of 95 mm and 125 mm from the center of the seed tray. The four arcs form the outline of the disturbing tooth and are plotted as shown in Figure 10.

The seed-disturbing teeth break the stable state of garlic seed accumulation. At the same time, they can be used as a baffle to provide thrust to the garlic seeds and cooperate with the hole in groups, so that the garlic will not be dislodged from the hole by the force of other garlic seeds. According to the average width of garlic seeds and agronomic requirements, the distance between the hole and the disturbing teeth should be less than the minimum width of garlic seeds, and 10 mm is chosen in this paper.

2.3. Simulation Model Building

2.3.1. Analysis of Seed-Disturbing Tooth Auxiliary Perturbation Seed

To analyze the effect of the number of seed-disturbing teeth on the forces acting on the seeds, the discrete element method was used to investigate the forces on the seeds under 9, 12, and 15 teeth operations, respectively [27]. EDEM is the leading general-purpose CAE software for solving discrete element problems using discrete element simulation, modeling, and analysis of granular bodies. It is widely used in agricultural engineering [28]. The materials and parameters of each component of the garlic seed and seed rower [16,29] are shown in

Table 2. Material parameters.

Materials	Poisson’s Ratio	Shear Modulus/Pa	Density kg/m3
Garlic seeds	0.25	1 × 108	1080
Resin material (the seed tray and seedbox)	0.36	1.2 × 108	1420
Polyurethane PU elastic sheet (seed disturbing teeth)	0.33	2.21 × 108	1072

and

Table 3. Simulation parameters.

Contact Form	Crash Recovery Factor	Static Friction Coefficient	Coefficient of Dynamic Friction
Garlic seeds—Garlic seeds	0.487	0.503	0.108
Garlic seeds—Resin material	0.36	0.34	0.06
Garlic seeds—Polyurethane PU elastic sheet	0.32	0.21	0.11

.

In order to analyze the effect of different operating speeds on the force of garlic seeds, speed levels of 0.5, 1.0, and 1.5 km/h were selected in this paper. To ensure the same spacing, the rotational speeds of the seed tray with different numbers of teeth were set, which are shown in

Table 4. The rev of a sucking-seed plate with a different tooth.

Operating Speed	The Number of Teeth Is 15	The Number of Teeth Is 12	The Number of Teeth Is 9
0.5 km/h	6 rpm	7.5 rpm	10 rpm
1 km/h	12 rpm	15 rpm	20 rpm
1.5 km/h	18 rpm	22.5 rpm	30 rpm

.

Set the simulation time to 10 s, set the generation of 600 pieces of garlic seeds to be completed within 1 s, and set the corresponding rotation speed of the seed tray for each group of seed-disturbing teeth from 2 s to 10 s of simulation. The simulation process is shown in Figure 11.

The average speed values of garlic at each moment of the stable working time of 3~6 s were selected and plotted in Figure 12. It can be seen from Figure 12 that with the increase in operating speed, the average speed of the three tooth numbers increases. The average speed is the embodiment of the disturbance effect, that is, 1.5 km/h shows the best disturbance effect under the three operating speeds. When the operating speed is 0.5 km/h, the average speed of 9 teeth fluctuates up and down at 0.05 m/s; the average speed of 12 teeth fluctuates up and down at 0.04 m/s, and the average speed of 15 teeth fluctuates up and down at 0.03 m/s. When the operating speed is 1 and 1.5 km/s, the average speed of 9 teeth is the fastest. This means that the disturbance effect of 9 teeth is the best.

2.3.2. Analysis of Hole-Adsorbed Seed

Under other conditions being the same, the airflow distribution on the surface of the hole determines the adsorption effect of the hole, and the equation of the adsorption force of the airflow on the surface of the garlic species [21], is

$$F=\frac{1}{2}C\rho S{V}^2$$

(13)

where:

• $F$—Adsorption force of airflow on garlic seeds, N;
• $C$—Air resistance coefficient;
• $S$—Garlic seed contact area, m². This is the area of the hole;
• $V$—Relative velocity of airflow, m/s;
• $\rho$—Air density, kg/m³. Constant $\rho$ at a low relative velocity of airflow.

According to the above Equation (13), the adsorption force of the hole on garlic seeds is positively related to the contact area of garlic seeds and the square of the relative velocity of airflow. So, increasing the contact area of garlic seeds and the relative velocity of airflow is conducive to increasing the adsorption force of the hole on garlic seeds and improving the seed extraction effect of the seed tray.

The diameter of the hole directly affects the airflow distribution at the hole and then affects the adsorption effect of the hole on garlic seed. Computational Fluent Dynamics (CFD) is a computer-based numerical simulation to analyze the flow of a fluid in a flow field, which can visualize the physical information of the liquid as it flows and can solve complex fluid dynamics problems [30,31]. Fluent software is currently the most widely used commercial CFD software and is now also commonly used in agricultural engineering [32]. The FLUENT simulation analysis was conducted for the seed tray with the number of holes of 9 and the diameter of holes of 6 mm, 8 mm, and 10 mm. The airflow pressure, velocity, and turbulent kinetic energy clouds at the holes were obtained as shown in Figure 13. Then, the cloud diagram of the hole nearest to the negative pressure outlet was expanded along its diameter in the vertical plane to analyze the airflow distribution at the holes of the three seed tray. According to Figure 13a, the pressure cloud diagrams of different hole diameters show that the pressure in the hole in the seed tray gradually increases clockwise. From the cloud diagram of the vertical surface of the nearest hole along the diameter of the negative pressure outlet, it can be seen that the closer the distance to the hole opening, the higher the pressure. As the diameter of the orifice increases (D = 6~10 mm), the stress in the hole also increases. In Figure 13b, the flow velocities of 6 mm and 10 mm diameter holes do not differ much and gradually increase in a clockwise direction, with flow velocities mainly concentrated in 27~65 ms⁻¹, and 8 mm diameter holes are yellow and red, with larger flow velocities in 65~88.57 ms⁻¹. Figure 13c shows that the turbulent energy of 6 mm holes is the largest and more turbulent among the three diameter holes, and the turbulent energy of 8 mm and 10 mm holes are close and more stable. According to Figure 13a–c, the pressure and flow velocity of the third hole reach the maximum value, and the turbulence energy reaches the minimum value. The pressure and flow velocity of the left half of the orifice is larger than those of the right half, and the turbulent energy is more minor. The left half of the orifice corresponds to the seed filling area and seed cleaning area of the seed releaser, so that the airflow distribution can ensure the stability of seed filling and at the same time garlic seed adsorbed in the orifice will not fall off during seed cleaning. In summary, the airflow distribution of an 8 mm diameter hole is better for the adsorption of garlic seeds.

Through the FLUENT simulation test of the seed tray with each hole diameter, the average velocity of 9 holes was counted respectively, and the average velocity of holes with diameters of 6 mm, 8 mm, and 10 mm were 88.4 m/s, 80.6 m/s and 69.1 m/s, respectively, and according to the Formula (13) of the adsorption force of airflow on the surface of garlic seeds, it can be obtained that the adsorption force from large to small corresponds to the hole diameters 8 mm, 6 mm and 10 mm. It is therefore more suitable to choose 8 mm as the diameter of seed rower.

2.4. Experimental Design and Evaluation Methods

The above-measured garlic seeds were used as test materials. The air suction garlic seed metering device was installed on a JPS-12 seed disperser test stand (produced by China Harbin Bona Technology Co., Ltd., Harbin, China, with a seedbed belt speed of 1.5~12 km/h and seed dispersal shaft speed of 10~150 rpm), and other equipment required for the test were an electronic barometer (measuring range ±35 kPa, accuracy ±0.3% FSO) and an i-speed3 high-speed camera (produced by Japan Olympus company production, using cmos 1280 × 1024 sensor, speed up to 2000 frames/second full resolution recording), etc., the test equipment and installation location as shown in Figure 14.

To test the seeding performance of this device, 250 consecutive garlic seeds were randomly selected for each group of tests to measure statistics and repeated three times. The test results were averaged and recorded. Since the pass rate + missed seeding rate + reseeding rate = 100%, two of them are known to obtain the third one, so the pass rate $Y_1$ and missed the seeding rate $Y_2$ were selected as evaluation indicators to measure the seeding performance. The evaluation index formula [33] is as follows.

$$Y_1=\frac{m_1}{M^{\prime }}\times 100\%$$

(14)

$$Y_2=\frac{m_2}{M^{\prime }}\times 100\%$$

(15)

where:

• $Y_1$—Pass seeding rate, %;
• $Y_2$—Missed seeding rate, %;
• $m_1$—Number of garlic seeds where the distance between two adjacent garlic seeds is greater than 1.5 times the theoretical plant distance;
• $m_2$—Number of garlic seeds where the distance between two adjacent garlic seeds is greater than 0.5 times the theoretical plant distance;
• $M^{\prime }$—The total number of garlic species counted in this paper is 250.

The operating parameters are shown in Table 4. The number of tooth and hole combinations, the diameter of holes, the operating speed, and the negative working pressure were selected as the test factors, and a four-factor, a three-level orthogonal test was conducted on the device, as shown in

Table 5. Experimental design and results.

Serial Number	Factors				Response Values
	The Number of Tooth and Hole ${\mathit{X}}_1$	Diameter of Hole ${\mathit{X}}_2/\mathbf{m}\mathbf{m}$	Operating Speed ${\mathit{X}}_3 \left(\mathbf{k}\mathbf{m}/\mathbf{h}\right)$	Negative Working Pressure ${\mathit{X}}_4/\mathbf{k}\mathbf{P}\mathbf{a}$	Pass Rate ${\mathit{Y}}_1/\%$	Missed Seeding Rate ${\mathit{Y}}_2/\%$
1	1	1	0	0	88.2	6.5
2	−1	1	0	0	86.7	7.8
3	1	−1	0	0	87.5	7.7
4	−1	−1	0	0	83.4	9.5
5	0	0	1	1	79.4	10.5
6	0	0	−1	1	81.3	10.6
7	0	0	1	−1	81.5	9.2
8	0	0	−1	−1	82.7	8.4
9	1	0	0	1	87.6	8.2
10	−1	0	0	1	81.4	8.6
11	1	0	0	−1	89.3	5.3
12	−1	0	0	−1	85.7	6.8
13	0	1	1	0	81.8	9.3
14	0	−1	1	0	80.4	8.6
15	0	1	−1	0	82.8	8.5
16	0	−1	−1	0	81.5	12.2
17	1	0	1	0	84.6	7.1
18	−1	0	1	0	78.4	8.2
19	1	0	−1	0	85.4	7.8
20	−1	0	−1	0	82.3	10.5
21	0	1	0	1	87.6	8.1
22	0	−1	0	1	82.6	10.5
23	0	1	0	−1	87.3	9.5
24	0	−1	0	−1	84.1	9.8
25	0	0	0	0	87.5	8.8
26	0	0	0	0	86.9	8.7
27	0	0	0	0	87.9	8.9
28	0	0	0	0	86.1	9.5
29	0	0	0	0	87.6	8.5

.

3. Results and Discussion

3.1. Effect of Factors on the Effectiveness of Seeding

In the paper, 29 sets of trials were conducted using the 4-factor, 3-level experimental scheme, which included 5 zero-point estimation errors and 24 analysis factors, where $X_1$, $X_2$, $X_3$ and $X_4$ denote the coded values of each factor. The test data were imported into Design-Expert 8.0.6 data processing software, and multiple regressions were fitted to the test data to obtain the regression equations for the pass rate $Y_1$ and the missed seeding rate $Y_2$, as follows:

$$\begin{array}{c}{Y}_1=87.2-2.06X_1-1.24X_2+0.82X_3-0.89X_4-0.65X_1{X}_2+0.77X_1{X}_3-0.65X_1{X}_4+0.025X_2{X}_3\\ -0.45X_2{X}_4+0.17X_3{X}_4+0.067X_1^2-0.76X_2^2-4.73X_3^2-1.18X_4^2\end{array}$$

(16)

$$\begin{array}{c}{Y}_2=8.88+0.73X_1+0.72X_2+0.43X_3+0.63X_4+0.12X_1{X}_2+0.4X_1{X}_3-0.28X_1{X}_4+1.1X_2{X}_3+0.52X_2{X}_4\\ +0.22X_3{X}_4-1.41X_1^2+0.34X_2^2+0.71X_3^2+0.031X_4^2\end{array}$$

(17)

The data processing results and the analysis of variance of the regression equation are shown in

Table 6. Variance analysis of regression equation.

Source of Variance	Pass Rate				Missed Seeding Rate
	Sum of Squares	Degree of Freedom	F-Value	p-Value	Sum of Squares	Degree of Freedom	F-Value	p-Value
Models	246.68	14	19.29	**	47.28	14	5.72	**
$X_1$	50.84	1	55.66	**	6.45	1	10.93	**
$X_2$	18.50	1	20.25	**	6.16	1	10.44	**
$X_3$	8.17	1	8.94	**	2.17	1	3.67
$X_4$	9.54	1	10.44	**	4.69	1	7.94	*
$X_1{X}_2$	1.69	1	1.85		0.063	1	0.11
$X_1{X}_3$	2.40	1	2.63		0.64	1	1.08
$X_1{X}_4$	1.69	1	1.85		0.30	1	0.51
$X_2{X}_3$	2.500 × 10−3	1	2.737 × 10−3		4.84	1	8.20	*
$X_2{X}_4$	0.81	1	0.89		1.10	1	1.87
$X_3{X}_4$	0.12	1	0.13		0.20	1	0.34
$X_1^2$	0.029	1	0.032		12.83	1	21.74	**
$X_2^2$	3.73	1	4.08		0.76	1	1.29
$X_3^2$	145.33	1	159.10	**	3.23	1	5.47	*
$X_4^2$	9.08	1	9.94	**	6.167 × 10−3	1	0.01
Residuals	12.79	14			8.27	14
Loss of proposed items	10.75	10	2.11	0.2461	7.70	10	5.42	0.0588
Error	2.04	4			0.57	4
Total	259.47	28			55.55	28

Note: p < 0.01 (Extremely significant, **); 0.01 < p < 0.05 (Significant, *).

. the p-value of the pass rate and missed seeding rate of the regression model are less than 0.01, which means that the regression model is extremely significant, and the p-value of the regression model loss-of-fit term is greater than 0.05, which means that the loss-of-fit term is not significant, so it is known that the model fits well.

In the pass rate regression equation, the regression terms with highly significant effects (p < 0.01) are $X_1$, $X_2$, $X_3$, $X_4$, $X_3^2$, and $X_4^2$, and the effects of the remaining terms are insignificant. The degree of influence of the four factors on the pass rate, in descending order, is the number of tooth and hole combinations, hole diameter, negative working pressure, and operating speed. In the regression equation of the sowing rate, the regression terms with highly significant (p < 0.01) effects are $X_1$, $X_2$, $X_4$, $X_1^2$, and the regression terms with significant (0.01 < p < 0.05) effects are $X_2{X}_3$, $X_3^2$, and the rest of the terms are insignificant, and the effects of the four factors on the sowing rate are, in descending order, the number of tooth and hole combinations, hole diameter, negative working pressure, and operating speed.

(1)

The influence of the hole diameter

From Figure 15a,d, and Figure 16a, when the working speed and negative pressure are at the central level, the influence of the number of tooth and hole combinations and the diameter of the hole on the pass seeding rate are related. When the diameter of the hole is fixed, with the increasing number of combinations, the pass seeding rate gradually decreases; when the number of combinations is fixed, with the increasing diameter of holes, the pass seeding rate first increases and then decreases. From Figure 16d, when the operating speed is less than 1 km/h, the hole diameter is negatively correlated with the rate of missed seeding, and when the operating speed is greater than 1 km/h, the hole diameter is positively correlated with the rate of missed seeding. In Figure 16e, when the negative working pressure is less than 5.5 kPa, the hole diameter is positively correlated with the missed seeding rate, and when the negative working pressure is greater than 5.5 kPa, the missed seeding rate is the first to decrease and then increase with the increasing hole diameter.

(2)

The influence of the number of tooth and hole combinations

From Figure 15a–c, it can be concluded that the higher the number of tooth and hole combinations, the lower the pass rate. From Figure 16a–c, it can be concluded that as the number of tooth and hole combinations becomes larger, the missed seeding rate increases and then decreases.

(3)

The influence of operating speed

From Figure 15b,d,f can be obtained the influence of operating speed, with 1 km/h as the dividing line. As the operating speed increases, the qualified rate is first increased and then decreased, and Figure 16b,f can be obtained. As the operating speed increases, the missed seeding is first reduced and then increased, as in Figure 16d, when the hole diameter is less than 8 mm, the missed seeding rate gradually decreases as the operating speed keeps rising, when the hole diameter is greater than 8 mm, the missed seeding rate gradually increases as the operating speed keeps growing.

(4)

The influence of negative working pressure

From Figure 16c,e,f, it can be obtained that the negative working pressure is negatively correlated with the missed seeding rate. In Figure 15c,e,f, the pass rate increases and then decreases as the negative working pressure increases, with −5.5 kPa as the dividing line.

Hole diameter, tooth and hole combination number, operating speed, and negative pressure are complementary to each other and match each other to make the passing rate higher and the missed seeding rate lower. From the above analysis of the response surface [34], it can be obtained that the number of combinations is 9~12, the diameter of holes is 6~8 mm, the operating speed is 0.8~1.2 km/h, and the negative pressure is 4.5~6 kPa.

3.2. Parameter Optimization and Validation

With the lowest missed seeding rate and the highest pass rate as the evaluation index, the best seeding effect of the device is explored, and the four influencing parameters of the number of tooth and hole combinations, the hole diameter, the operating speed, and the negative working pressure are optimized [35], and the optimization function as shown in Equation (18).

$$\{\begin{array}{c}\max Y_1\\ \min Y_2\\ -1<X_1<1\\ -1<X_2<1\\ -1<X_3<1\\ -1<X_4<1\end{array}$$

(18)

The optimal combination of parameters was analyzed as follows: The number of tooth and hole combinations was 9, the diameter of the hole was 7.24 mm, the operating speed was 1.04 km/h, and the negative working pressure was −5.53 kPa; the model predicted a pass seeding rate of 89.1% and a missed seeding rate of 6.17%.

In order to verify the accuracy of data optimization analysis, the optimized parameters were verified. The operation speed of the machine was adjusted to 1 km/h, the rotational speed of the seeding disc was 19.3 r/min, and the working negative pressure was adjusted to −5.5 KPa, and the test was repeated five times, and the results were counted as shown in

Table 7. Optimization of test results.

Serial Number	Passing Rate	Missed Seeding Rate
1	88.5	6.3
2	88.8	6.7
3	89.3	5.9
4	87.7	6.2
5	88.4	6.6
Average value	88.54	6.34

. When the number of tooth and hole combinations is 9, the hole diameter was 7.2 mm, the working speed was 1 km/h, and the working vacuum pressure was −5.5 KPa, the average pass seeding rate of the 5 tests was 88.54%, and the average missed seeding rate was 6.34%, which met the agronomic requirements of garlic sowing.

3.3. Field Trails

The seeding test platform mainly includes seed rower, air blower, land wheel, pulley and frame, etc. The test stand is traction type, connected to the tractor by three-point suspension, the pulley is mounted on the spline shaft, and the spline shaft is connected to the tractor power take-off (PTO) through the universal joint to drive the pulley rotation. The power is transmitted to the air blower through the pulley, and the air blower rotates to provide continuous and stable air pressure for the seed rower through the air pipe.

The test site was located at the experimental base of Anhui Agricultural University’s Nongcui Park, and the tractor selected was Dongfeng DF-1004. The seedbed was prepared before the test [36] to improve soil looseness and flatness, and the soil firmness and average moisture content were obtained by measurement as 14.96 kPa, and 6.82%, respectively, and the test site is shown in Figure 17.

The optimized parameters were used to conduct field trials, and the trials were repeated three times to measure the spacing of the tests when the work was smooth, as shown in Figure 17. The results of the three tests were counted, and the average evaluation index of the practices was calculated, and a pass rate of 87.83% and a miss rate of 6.85% were obtained, which satisfied the requirements of garlic cultivation.

4. Conclusions

(1)

An air suction garlic seed metering device with disturbance assistance was designed in order to improve garlic metering quality. Through the curve fitting of garlic seed profile and static analysis, the initial dimensions of the critical components were determined. Among them, the diameter and number of holes were 6, 8, and 10 mm, and 9, 12, and 15, respectively.

(2)

Based on discrete element simulation results, when the simulated seed metering device was at a forward speed of 0.5, 1.0 and 1.5 km/h, the population disturbance was best with 9 shaped holes. On this basis, fluid dynamics simulation was conducted to determine the effect of adsorption in different diameters of shaped holes. The simulation results showed that the airflow distribution of an 8 mm diameter hole is better for the adsorption of garlic seeds

(3)

Based on a bench test and parameters’ optimization results, the optimal parameter combination was as follows: the diameter of holes was 7.24 mm, the operating forward speed was 1.04 km/h and the negative pressure was −5.53 kPa. The qualified seeding index and miss seeding index were 88.54% and 6.34% respectively under the above combination parameters. The error between field test results and bench test results were 0.71% and 0.51%, which showed the air suction garlic seed metering device was within a reasonable range and could be used for actual seeding operations.