Design and Experiment of Double-Row Seed-Metering Device for Buckwheat Large Ridges

Abstract

This article focuses on the low accuracy, poor stability, and other shortcomings of the traditional outer-groove buckwheat seed-metering wheel. A wheel-type large-ridge double-row seed-metering device with inner seed-filling holes was designed. The seed-metering device’s structural composition, working principle, and main technical parameters are clarified. The structural parameters of the seed-metering device shell and the seed-metering wheel are determined based on the force analysis, movement trajectory, and physical characteristics of the buckwheat grains. This experiment uses the JPS-12 metering device performance experiment bench for bench experimenting. The experiment uses the seed-metering device’s rotation speed, the seed position’s height, and the seed wheel’s aperture as experiment factors. Based on the experiment indicators of the qualified rate of number of holes and the grain damage rate, we used Design-Expert12 software to design single-factor, response surface, and verification experiments. The experiment results show that the best parameter combination is a seed-metering device rotation speed of 67 r/min, a seed position height of 115 mm, and a seed wheel aperture of 8 mm. In the optimal parameters, the qualified rate of the number of holes is 90.23%, and the grain damage rate is 0.62%. The experiment indicators meet the operational requirements of the buckwheat seeding device. The design and experimenting of the buckwheat large-ridge double-row seeding device provide a reference for further research on buckwheat seeding.

1. Introduction

Buckwheat is one of the unique multigrain crops in southwest China, and it is also widely cultivated and spread around the world [1]. Buckwheat has the characteristics of a short growth period, drought tolerance, cold tolerance, and barren resistance. It can not only be used as an important nutrient source of fatty acids and mineral elements [2], but also contains anti-starch, protein, and phenolic substances, which help to prevent the occurrence of a variety of chronic diseases [3]. Therefore, buckwheat is of great significance in the fields of agricultural production, medicine, and nutrition [4].

Traditional buckwheat planting mostly uses single-row ridge cultivation technology (cultivation technique of single-row ridge), which has low efficiency, low yield, and other problems. Double-row ridge technology is an effective way to improve soil utilization and increase crop yields, increasing yields by 15–30% compared to single-row ridge technology [5,6,7]. At present, the traditional external grooved wheel seed-metering device is used in most of the double-row cultivation methods [8]. However, this seed-metering device has low discharge accuracy and poor stability, which seriously affects the seeding quality of cultivated wheat. Therefore, the design of an inner seed-filling-type hole wheel seed-metering device [9], can help realize the “one device, two rows” sowing operation for the buckwheat yield, which is of great significance.

Bu et al. designed a 2BF-3 large-ridge double-row buckwheat seeder. The seed-metering device of this seeder adopts a groove wheel type seed-metering device, which realizes double rows in one ridge, separate application of seeds and fertilizers, and a precise and small amount of sowing. Field trials show that the operation quality is excellent, can meet agronomic requirements, and adapts to the needs of sowing in mountainous and dry lands, but it has low displacement accuracy and poor stability [10]. Li et al. used the discrete element method to design a seed-metering device for an external groove wheel-type buckwheat seeder and performed parameter simulation optimization. Orthogonal experiments were conducted on three typical buckwheat seeds during the simulation process. The experiment results show that the designed seed-metering device can meet the sowing rate requirements for the three types of buckwheat seeds, but vibration affects its uniformity [11]. Ru et al. designed a centrifugal seed-metering device for buckwheat based on a vertical-type disc seed-metering device. Compared with traditional vertical disc seeders, it realizes high-speed seeding and allows centrifugal force to participate in the three processes of seed filling, seed protection, and seed cleaning. It has a simple structure and small size and can be adapted to work in mountainous areas and residential areas, but its replay rate is large and its stability is poor [12]. Ye et al. designed a gas chamber rotary buckwheat precision seed-metering device to solve the traditional gas suction seed-metering device’s negative pressure gas chamber’s poor sealing, higher power consumption, and other issues. With small rotating energy consumption, good airtightness, and other characteristics, it has the disadvantages of low precision, seed breakage, complex operation, and not adapting to a variety of seeds [13]. Li et al. designed a dual-row pneumatic precision planter to solve the problems of easy seed damage, low seed discharge efficiency, and poor pass rate, but it has the disadvantages of poor adaptability, inaccurate seed discharge, complicated operation, and difficult maintenance [14].

For this purpose, we have determined a seed-metering device, seed-metering device shell, and seed wheel structural parameters through buckwheat seed force analysis, trajectory, and physical properties, and have designed a medial filling-type hole wheel seed-metering device, which can realize the “one device and two rows” qualifications of the seed-metering device, which is suitable for raising the wheat by two rows in one large-ridge seeding.

2. Materials and Methods

This experiment uses the JPS-12 metering device performance experiment bench for bench experimenting. The experiment refers to the industry standard NY/T 1143-2006 “Technical specifications of quality evaluation for drills” [15]. National standard GB/T 6973-2005 “Testing methods of single seed drills (precision drills)” [16] and national standard GB/T 9478-2005 “Testing methods of sowing in lines” [17,18] are among the main performance indicators of the hill-drop planter, and the qualified rate of the number of holes and the damaged rate of seeds were selected as the evaluation criteria. Three experimental factors were selected, using Design-Expert12 software to design single-factor, response surface, and verification experiments [19]. According to the test results, it is verified whether the designed seed feeder can meet the operation requirements of the buckwheat seed feeder.

2.1. Physical and Mechanical Properties of Buckwheat Seeds

Buckwheat seeds are small in size and triangular in shape, and their physical characteristics have a great influence on the quality of sowing. The basic physical properties of a seed include thousand grain weight, size, angle of rest, angle of sliding friction, and coefficient of sliding friction. Size includes the length, width, and height of the seed. To obtain the basic physical property parameters, we randomly selected 100 undamaged buckwheat seeds for measurement and repeated the measurement for five groups. The measurement results show that the length of the grain l is 5.86~6.74 mm, the width b is 3.32~4.33 mm, and the thickness a is 3.17~4.53 mm. Measurements of the physical characteristics of buckwheat yielded the average parameters of its physical characteristics, as shown in

Table 1. Table of average parameters of physical properties of buckwheat grain.

Thousand-Grain Weight (g)	Length (mm)	Width (mm)	Thickness (mm)	The Angle of Repose (°)	Sliding Friction Angle (°)	Coefficient of Sliding Friction
27.62	5.86–6.74	3.32–4.33	3.17–4.53	30.50	25.6	0.478

.

2.2. Overall Design of Seed-Metering Device

The 3D structure of the buckwheat large-ridge double-row seed-metering device is shown in Figure 1. The 2D structure of the buckwheat large-ridge double-row seed-metering device is shown in Figure 2a. It is mainly comprised of 1. a conveying pipe, 2. seed-metering device housing, 3. a seed-limiting device, 4. a rolling bearing, 5. a seeding shaft, 6. a seeding wheel, and 7. a seeding sprocket.

The structural diagram of the seed-limiting device is shown in Figure 2b. It consists of a rubber seed scraper and two seed-limiting plates. The material of the seed scraper is rubber.

The operation process of the seed-metering device includes three stages: seed filling, seed protection, and seed-metering, as shown in Figure 2c [20]. During operation, buckwheat grains are transported from the seed box to the seed-filling area through conveyor pipe 1. The seed flow is controlled by seed-limiting device 3. Under the action of gravity and inter-species force, the seeds are filled into the holes of seed-metering wheel 6 to complete the seed filling. The power of the ground wheel drives seeding shaft 5 and seeding wheel 6 to rotate through seeding sprocket 7, bringing the seeds in the hole to the seed protection area. At this time, through the action of the flexible rubber seed scraper on the seed-limiting device 3, the excess seeds can be scraped above the hole and returned to the seed-filling area. The seeds in the hole enter the seeding area with the rotation of seeding wheel 6. Enter the seeding pipe through the seeding port on the seeding device housing 2 to complete the seeding process.

The main technical parameters of the buckwheat large-ridge double-row seed-metering device are shown in

Table 2. Technical parameters of buckwheat large-ridge double row metering device.

Projects	Units	Technical Parameters
structure size (L × W × H)	mm	150 × 135 × 185
structural weight	kg	4.15
structure type		inside seed filling type orifice wheel type
number of single-row holes	number	10
seed discharge wheel diameter	mm	φ144
hole type		inverted cone
hole diameter	mm	φ8
number of hole sets	groups	2
seed-limiting device structure type		arch type

.

2.3. Seed-Metering Device Structural Design and Theoretical Analysis

2.3.1. Seeder Housing Design

The structural diagram of the seed-metering device housing is shown in Figure 3. The seed-metering device casing adopts a barrel-shaped structure. The bearing housing hole is arranged inside the center. Two sets of bolt holes evenly distributed on the bottom of the barrel form fixed connections with the frame and delivery pipe, respectively. There is a rectangular seeding opening in the circumferential direction of the housing. There is a φ35 mm seed inlet at the end, which cooperates with the seed-metering wheel to form a seed-filling area, a seed protection area, and a seed-metering area [21].

When the research object is a single-seed seeding filled with holes, the seeds enter the seeding area from the seed protection area as the seeding wheel rotates. When discharged from the seed discharge port, it has an initial velocity $v$ along the tangential direction, and an analysis diagram of the grain discharge movement trajectory shown in Figure 4 is constructed [22]. When the seeds leave the seed-metering device, they are affected by gravity. Under the action of gravity, the grains are thrown obliquely with an initial velocity of $v$. To ensure that the seeds can be discharged smoothly from the seeding opening, the opening angle $\beta$ of the seeding opening can be designed through the following Equations (1)–(3).

The initial speed $v$ when the seeds leave the seed-metering device is the linear speed of the seed-metering wheel. According to the buckwheat-sowing hole spacing of 20 cm and the seeder operating speed of 4 km/h, the initial velocity $v$ when the grains leave the seed-metering device is calculated through Equation (1).

$$\{\begin{array}{l}v=\frac{n_d\cdot \pi \cdot D}{60}\\ n_d=i\cdot \frac{60v_m}{\pi \cdot D}\\ i=\frac{n_d}{n_D}=\frac{\pi \cdot D\cdot (1+\delta )}{S\cdot z_1}\end{array}$$

(1)

In Equation (1), $n_d$ is the seeder rotation speed (r/min); $n_D$ is the ground wheel rotation speed (r/min); $D$ is the diameter of the ground wheel (m), and the value is 0.4 m; $i$ is the transmission ratio between the seed-metering device and ground wheel; $v_m$ is the seeding operation speed (m/s), and the value is 4 km/h (approximately 1.1 m/s); $\delta$ is the ground wheel slip coefficient, and the value is 0.1; $S$ is the hole spacing (m), and the value is 0.2 m; and $z_1$ is the single-row hole quantity, and the value is 10.

Calculate the highest point s of grain throwing according to Equation (2).

$$\{\begin{array}{l}s=v_{2}t-\frac{1}{2}g{t}^2\\ v_2=v\cdot \cos \theta \\ t=\frac{v_2}{g}\end{array}$$

(2)

In Equation (2), v₂ is the initial velocity of the grains leaving the seed-metering device in the vertical direction (m/s); t is the time it takes for the seeds to reach their highest point (s); and g is the gravity acceleration, and the value is 9.8 m/s².

According to the geometric relationship shown in Figure 4, the calculation equation for the opening angle β is shown in Equation (3).

$$\{\begin{array}{l}\beta ={\cos }^{-1}(\frac{s_1}{R})-\theta \\ \theta ={\cos }^{-1}(\frac{s_2}{R-h_1})\\ s_1\le s_2-s\end{array}$$

(3)

In Equation (3), θ is set to ${40}^{°}$; s₁ is the vertical distance between the top of the opening and the center of the seed-metering device (m); s₂ is the vertical distance between the bottom of the opening and the center of the seed-metering device (m); R is the seeder housing radius (m), and the value is 0.078 m; h₁ is the seeder housing thickness (m), and the value is 0.006 m; and s is the highest point at which the seed is thrown (m).

According to the calculation, the initial velocity is when the seeds leave the seed-metering device $v=0.76$ m/s. The highest point at which the seed is thrown $s=17.29$ mm. Calculate the opening angle of the seeding port $\beta \ge {20.95}^{°}$, so $\beta ={21}^{°}$.

During seeding, the seeds enter the seeding area from the seed protection area as the seeding wheel rotates. When discharged from the seed discharge port, it makes a parabolic motion. In order to reduce the situation where the seeds cannot be discharged and the seeds are stuck, the shape of the seed discharge opening is designed according to the movement trajectory of the seeds. As shown in Figure 5, the chamfer $\alpha$ of the seed discharge opening below can allow the buckwheat grains to be discharged in time. It is easier to expel all the buckwheat grains and reduce the problem of being unable to expel them. The chamfer $\alpha$ of the upper seed discharge port can reduce the seed jam caused by the extrusion and collision of buckwheat grains with the upper wall of the seed discharge port during the discharge process. Therefore, designing the seed discharge opening as a parallelogram can effectively reduce the situation where the seeds cannot be discharged, and the seeds are stuck.

The size of the chamfer $\alpha$ of the seeding port is designed to be ${40}^{°}$.

2.3.2. Seed Displacement Wheel Design

The structure of the large-ridge double-row seeding wheel is shown in Figure 6. Its main structural parameters include seed wheel diameter, hole shape, hole diameter, hole depth, and number of holes. The schematic diagram of the hole is shown in Figure 6c.

The hole shape and size of the seeding wheel directly affect the seeding effect. The design is to prevent excess seeds from falling into the seed ditch and reduce damage to the seeds during the seeding process. The shape of the hole is designed to be an inverted cone. The diameter $d$, depth $H_2$, and height $h$ of the hole column area should be adapted to the size of the buckwheat grains.

When there are (3 ± 1) buckwheat seeds per hole, the hole diameter $d$ is calculated according to Equation (4). In order to ensure that the seeds can completely enter the hole, the hole depth $H_2$ is calculated according to Equation (5). In order to reduce seed jamming, the hole cylinder height $h$ should be smaller than the radius of the buckwheat grain so that the center of the buckwheat grain can enter the cone area. Therefore, the hole cylinder height $h$ is calculated according to Equation (6) [23,24].

$$d=l_{\max }+\Delta \cdot a\cdot b$$

(4)

$$H_2=1.2\cdot l_{\max }$$

(5)

$$h\le \frac{l_{\min }}{2}$$

(6)

In Equations (4)–(6), $d$ is the type hole diameter (mm); l is buckwheat grain length (mm); Δ is the gap left, generally take 0.7~1.5; b is buckwheat grain width (mm); a is buckwheat grain thickness (mm); $H_2$ is the hole depth (mm); and h is the hole cylinder height (mm).

Calculated: d = 7.44–8.24 mm, $H_2$ is 8.088 mm, and $h\le 2.93$ mm. Take d = 8 mm, $H_2$ = 8 mm and, h = 2 mm.

The number of type holes is affected by the seeding wheel’s diameter and the type hole’s diameter. When the diameter of the seeding wheel and the diameter of the hole are constant, the greater the number of holes, the weaker the structural strength of the seeding wheel, and the worse the seed-filling performance. The spacing between the holes shall be subject to meeting the strength requirements. Calculated based on the hole diameter of 0.008 m, the buckwheat sowing hole spacing is 15 cm and the seeder operating speed is 4 km/h. Then, the number of holes in the large-ridge double-row seeding wheel can be calculated according to Equation (7).

$$\{\begin{array}{l}{z}_2=\frac{\pi \cdot d_x\cdot v_m}{S\cdot v_p}\\ v_p\le (d-\frac{2}{3}{l}_{\max })\cdot \sqrt{\frac{g}{b_{\max }}}\end{array}$$

(7)

In Equation (7), $z_2$ is the total number of holes; $d_x$ is the seed wheel diameter (m), and the value is 0.144 m; $v_m$ is the working speed (m/s), and the value is 4 km/h (approximately 1.1 m/s); S is the hole spacing (m), and the value is 0.15 m; $v_p$ is the ultimate linear speed of the seed-metering device (m/s); d is the type hole diameter (m); l_max is the maximum length of grains (m), and the value is 0.00674 m; and $b_{\max }$ is the maximum width of grains (m), and the value is 0.00433 m.

Calculated: The limit linear speed of the seed-metering device is $v_p\le 0.163$ m/s, and the number of holes is z₂ ≥ 19.88, take z₂ = 20. Therefore, the number of shaped holes in a large-ridge double-row seeding wheel is 20, and the number of single-row shaped holes is 10.

2.4. Seeding Performance Experiment

2.4.1. Experiment Materials and Equipment

Using buckwheat as the material, the experiment was conducted in March 2023 at the Agricultural Machinery Laboratory of the College of Agricultural Engineering of Shanxi Agricultural University using the JPS-12 seed-metering performance experiment bench as the experiment equipment to conduct a bench experiment on the buckwheat seed-metering device [25]. The experiment device is installed, as shown in Figure 7a, to simulate field operation conditions. Figure 7b shows the overall structure of the seeder.

2.4.2. Experimental Measurement Indicators and Methods

The experiment refers to the industry standard NY/T 1143-2006 “Technical specifications of quality evaluation for drills”. National standard GB/T 6973-2005 “Testing methods of single seed drills (precision drills)” and national standard GB/T 9478-2005 “Testing methods of sowing in lines” are among the main performance indicators of the hill-drop planter, and the qualified rate of the number of holes $A$ (≥85%) and the damaged rate of seeds $B$ (≤1.5%) were selected as the evaluation criteria. This method is calculated using Equations (8) and (9).

$$A=\frac{n}{N}\times 100\%$$

(8)

$$B=\frac{m}{M}\times 100\%$$

(9)

In Equations (8) and (9), $A$ is the qualification rate of seed counting in the hole; $B$ is the seed damage rate; $n$ is the counting seeds in the hole number of qualified holes (number); $N$ is the total number of holes in the measurement area (number); $m$ is the amount of damage (g); and $M$ is the total discharge (g).

Design-Expert12 software is engineering software oriented to experimental design and related data analysis [26]. It can design correct and efficient experimental design plans. The Design-Expert12 software used the seeder metering device’s rotation speed, the seed position’s height, and the seeding wheel’s aperture as experiment factors. The single-factor experiment was completed using the qualification rate of the number of holes and the damage rate of the seeds as the performance indicators of the seed-metering device. Provide a reasonable numerical range for response surface experimenting through single-factor experimenting. Then, design a response surface experiment and perform data analysis on the experiment results. After determining the mathematical model between the experimental factors and indicators, perform a variance analysis. Finally, according to the results of the response surface experiment, the optimal experiment combination is determined by setting the optimization criteria, and a verification experiment is performed on the seed-metering device [27].

3. Results and Discussion

3.1. Single-Factor Experiment

The hole distances selected for the experiment are 10 cm, 13 cm, 16 cm, 19 cm, and 22 cm, and the corresponding seed-metering speeds are calculated according to Equation (1). The calculation results were 54.78, 42.14, 34.24, 28.83, and 24.9 r/min. According to the calculation results, the corresponding parameters were set in the test bench, and the hole spacing favorable for observation was tested.

The experiment results show that when the hole distance is 16 cm, the experiment results can be seen on the experiment bench. When the distance between holes is ≤16 cm, the distance between holes is too small, and the number of seeds in each hole cannot be observed on the experiment bench. When the distance between holes is ≥16 cm, the distance between holes is too large, and the number of holes is small, which is not conducive to observation [28].

Therefore, the bench experiment was conducted with a plant spacing of 16 cm.

3.1.1. Effect of Seeding Wheel Rotation Speed on the Performance of Seed-Metering Device

The experiment set the hole diameter of the seeding wheel to 8 mm and the grain mass to 50 g. There are five seed-metering device rotation speeds of 25, 40, 55, 70, and 85 r/min [29]. The corresponding sowing operation speeds are calculated according to Equations (10) and (11), which are 2.2, 3.5, 4.8, 6.1, and 7.4 km/h, respectively. Each group performs five experiments and takes the average value. The obtained data are shown in Figure 8.

Too low a rotational speed may cause seeds to fall slowly, resulting in uneven planting densities, while too high a speed may cause seeds to fall too quickly, which can easily result in seed breakage or buildup. It can be seen from Figure 8 that when the seed-metering device’s rotation speed is 55 r/min, the qualification rate of the number of holes is optimal, which is 85%. As the rotational speed of the seed-metering device increases, the grain damage first decreases and then increases. The minimum is at 55 r/min, which is less than 0.5% and meets the standard, and the maximum is at 85 r/min, reaching 0.75%.

Therefore, when the hole diameter of the seeding wheel is 8 mm, the grain mass is 50 g, and the seeding device’s rotation speed is 25–85 r/min, the performance of the seeding device is good. Moreover, the seed-metering device’s performance is optimal when the seed-metering device’s rotation speed is about 55 r/min.

3.1.2. Effect of Seed Position’s Height on the Performance of Seed-Metering Device

The experiment set the hole diameter of the seeding wheel to 8 mm and the rotation speed of the seeding device to 55 r/min. The seed position’s height is taken into five groups, as shown in Figure 9. Take the lowest point of the cylindrical part of the seed box as the origin and establish coordinates vertically upward in the positive direction, which are 40, 80, 120, 160, and 200 mm. Each group performs five experiments and takes the average value. The obtained data are shown in Figure 10.

When the seed volume is too low, the seed-metering device may exert too much pressure and friction, resulting in seed breakage. Friction and collision between seeds can also increase seed breakage when the seed volume is too high. It can be seen from Figure 10 that the qualification rate of the number of hole particles meets the standard when the seed height is 40–200 mm. Furthermore, the seed height is the highest at 120 and 200 mm. As the seed height increases, grain damage decreases and then increases, reaching a minimum of 120 mm.

Therefore, when the hole diameter of the seeding wheel is 8 mm, the rotation speed of the seeding device is 55 r/min, and the height of the seed position is 40–200 mm, the performance of the seeding device is good. The performance of the seed-metering device is optimal when the seed height is about 120 mm.

3.1.3. Effect of Seed Wheel’s Aperture on the Performance of Seed Feeder

The experiment set the grain mass to 50 g and the seed-metering speed to 55 r/min. There are five seeding wheel apertures, namely 6.5 mm, 8 mm, 9.5 mm, 11 mm, and 12.5 mm. Each group performs five experiments and takes the average value. The obtained data are shown in Figure 11.

It can be seen from Figure 11 that when the grain mass is 50 g and the seed-metering speed is 55 r/min, the seeding wheel aperture is only 8 mm, and it meets the relevant national standards.

3.1.4. The Results of Single-Factor Experiment

The fitting toolbox (cftool) in Matlab(R2020a) software is used to solve the functional relationship between the qualification rate of the number of holes $Y_1$, the seed damage rate $Y_2$, the seed-metering device’s rotation speeds $X_1$ [30], the seed height $X_2$, and the seeding wheel aperture $X_3$ as seen in

Table 3. The functional relationship between factors and indicators.

Functional Relationship	R-Square	RMSE
$Y_1=-9.877e^{-05}{X}_1{}^3+0.009312X_1{}^2-0.1725X_1+77.29$	0.6397	6.215
$Y_2=-1.481e^{-06}{X}_1{}^3+0.0005111X_1{}^2-0.04111X_1+1.463$	0.9946	0.01673
$Y_1=6.893e^{-20}{X}_2{}^3-8.929e^{-05}{X}_2{}^2+0.04643X_2+84$	0.6429	2.39
$Y_2=2.604e^{-08}{X}_2{}^3-4.464e^{-07}{X}_2{}^2-0.0008095X_2+0.872$	0.9953	0.004781
$Y_1=2.321X_3{}^3-70.15X_3{}^2+682.5X_3-2080$	0.9137	15.06
$Y_2=-0.01259X_3{}^3+0.417X_3{}^2-4.595X_3+17.53$	0.9978	0.04661

.

3.2. Response Surface Experiment

3.2.1. Experimental Design and Results

Since there is a certain degree of interaction between various factors, a response surface experiment was conducted to study the impact of the interaction between the three factors on the performance of the seed-metering device. Use Design-Expert12 software to design response surface experiments. The experiment is set up with three factors and three levels, and the experimental factors are coded as shown in

Table 4. Experiment factor coding.

Coded	Factor
	$\mathbf{Seeder} \mathbf{Rotation} \mathbf{Speed} {\mathit{X}}_1$/(r/min)	$\mathbf{Species} \mathbf{Height} {\mathit{X}}_2$/(mm)	$\mathbf{Seed} \mathbf{Wheel} \mathbf{Aperture} {\mathit{X}}_3$/(mm)
−1	40	80	8
0	55	120	9.5
1	70	160	11

[31]. The qualification rate of the number of holes and the damage rate of the seeds are used as the performance indicators of the seed-metering device [32].

Seventeen groups of experiments were designed using Box–Behnken in Design-Expert12 software. Each group of experiments was repeated five times, and the experiment results were obtained based on the average value. The experiment plan and experiment results are shown in

Table 5. Experiment plan and results.

Sequence Number	${\mathit{X}}_1$	${\mathit{X}}_2$	${\mathit{X}}_3$	$\mathbf{Qualified} \mathbf{Rate} \mathbf{of} \mathbf{Number} \mathbf{of} \mathbf{Holes} {\mathit{Y}}_1$/(%)	$\mathbf{Grain} \mathbf{Damage} \mathbf{Rate} {\mathit{Y}}_2$/(%)
1	0	0	0	40	0.73
2	0	−1	−1	94	0.79
3	−1	−1	0	30	0.73
4	0	1	1	20	0.66
5	−1	0	−1	94	0.81
6	0	1	−1	84	0.81
7	0	−1	1	34	0.64
8	1	0	−1	92	0.83
9	1	−1	0	54	0.76
10	0	0	0	58	0.72
11	0	0	0	44	0.73
12	1	1	0	42	0.78
13	1	0	1	38	0.68
14	0	0	0	60	0.71
15	−1	1	0	46	0.76
16	−1	0	1	22	0.66
17	0	0	0	44	0.74

.

3.2.2. Analysis of Results

Use the analysis function in Design-Expert12 software to perform a variance analysis on the experiment results. The analysis results are shown in

Table 6. Variance analysis table of pass rate of hole particle number.

Source	Sum of Squares	DF	F-Value	p-Value	Significance
Model	9147.73	9	16.33	0.0007	**
$X_1$	144.50	1	2.32	0.1715
$X_2$	50.00	1	0.8031	0.3999
$X_3$	7812.50	1	125.49	<0.0001	**
$X_1{X}_2$	196.00	1	3.15	0.1193
$X_1{X}_3$	81.00	1	1.30	0.2915
$X_2{X}_3$	4.00	1	0.0642	0.8072
$X_1{}^2$	7.67	1	0.1233	0.7359
$X_2{}^2$	99.04	1	1.59	0.2476
$X_3{}^2$	784.52	1	12.660	0.0093	**
Residual	435.80	7
Lack of Fit	103.00	3	0.4127	0.7535
Pure Error	332.80	4
Cor Total	9583.53	16

Note: “**” indicates extreme significance.

and

Table 7. Variance analysis table of seed damage rate.

Source	Sum of Squares	DF	F-Value	p-Value	Significance
Model	0.0525	9	71.59	<0.0001	**
$X_1$	0.0010	1	13.00	0.0087	**
$X_2$	0.0010	1	13.00	0.0087	**
$X_3$	0.0450	1	577.98	<0.0001	**
$X_1{X}_2$	0.0000	1	0.3211	0.5886
$X_1{X}_3$	0.0000	1	0.0000	1.0000
$X_2{X}_3$	0.0000	1	0.0000	1.0000
$X_1{}^2$	0.0028	1	35.86	0.0005	**
$X_2{}^2$	0.0001	1	1.79	0.2230
$X_3{}^2$	0.0002	1	2.46	0.1605
Residual	0.0005	7
Lack of Fit	0	3	0.0641	0.9761
Pure Error	0.0005	4
Cor Total	0.0507	16

Note: “**” indicates extreme significance.

. The regression equations of the pass rate of hole particle number $Y_1$ and seed damage rate $Y_2$ are obtained. The equations are Equations (10) and (11). The R-square for Equations (10) and (11) are 0.7738 and 0.9761, respectively.

$$Y_1=49.2-31.25X_3+13.65X_3{}^2$$

(10)

$$Y_2=0.726+0.0113X_1+0.0113X_2-0.075X_3+0.0258X_1{}^2$$

(11)

The F-value represents the significance of the entire fitting equation. The larger the F is, the more significant the equation is and the better the fit. The Model F-value of 16.33 implies the model is significant. There is only a 0.07% chance that an F-value this large could occur due to noise. The p-value indicates significance, a p-value < 0.01 indicates extreme significance, a p-value < 0.05 indicates significance, and p-values greater than 0.1000 indicate the model terms are not significant. The lack of fit F-value of 0.41 implies the lack of fit is not significant relative to the pure error.

It can be seen from Table 6 that the three factors of the experiment impact the qualification rate of the number of holes. According to the priority of influence, sorting is $X_3$, $X_3{}^2$, $X_1{X}_2$, $X_1$, $X_2{}^2$, $X_1{X}_3$, $X_2$, $X_1{}^2$, $X_2{X}_3$, where the p-value of $X_3$, $X_3{}^2$ is less than 0.01, indicating that $X_3$, $X_3{}^2$ has an extremely significant impact $Y_1$. The p-value of the remaining factors is more significant than 0.1, indicating that the impact of the remaining factors $Y_1$ is not significant.

The Model F-value of 71.59 implies the model is significant. There is only a 0.01% chance that an F-value this large could occur due to noise. The lack of fit F-value of 0.06 implies the lack of fit is not significant relative to the pure error. There is a 97.61% chance that a lack of fit F-value this large could occur due to noise. Non-significant lack of fit is good—we want the model to fit.

It can be seen from Table 7 that the three factors in the experiment have an impact on the grain damage rate. According to the priority of influence, sorting is $X_3$, $X_1{}^2$, $X_1$, $X_2$, $X_3{}^2$, $X_2{}^2$, $X_1{X}_2$, $X_1{X}_3$, $X_2{X}_3$, where the p value of $X_3$, $X_1{}^2$, $X_1$, $X_2$ is less than 0.01, indicating that $X_3$, $X_1{}^2$, $X_1$, $X_2$ has an extremely significant impact $Y_2$. The p value of the remaining factors is more significant than 0.1, indicating that the impact of the remaining factors $Y_2$ is not significant.

It can be seen from Table 6 and Table 7 that under the condition of significance level $\alpha =0.05$, the significance levels of the regression equation of the two indicators of the pass rate of the hole particle number and the seed damage rate are 0.0007 and <0.0001. Both significance levels are extremely significant, and the coefficients of determination $R^2$ of the regression equation are 0.9545 and 0.9893. The significance levels of the equation’s lack of fit terms are 0.7535 and 0.9761. The results are all greater than 0.1, indicating that the obtained regression equation fits the actual situation well, indicating no other important factors affecting the experiment indicators. The degree of influence of various factors on the pass rate of hole particles $Y_1$ and seed damage rate $Y_2$ of the buckwheat hole sowing seed-metering device, from primary to secondary, are seed wheel aperture, seed-metering speed, and seeding height.

It is important to study the influence of the interaction of various influencing factors on the pass rate of the hole particle number in the seed-metering device and the rate of seed damage. According to the experiment results, the Design-Expert12 software was used to create corresponding response surfaces, as shown in Figure 12 and Figure 13.

Figure 12a shows the impact of the interaction between the seed-metering speed and the seed position height on the qualification rate of the number of holes when the seed wheel aperture is 8 mm. When the rotational speed of the fixed seed-metering device remains unchanged, as the height of the seed position increases, the number of qualified seeds first increases and then decreases. When the height of the seed position increases, the pressure on the grains gradually increases, and the number of falling grains gradually increases, causing the number of qualified grains in the hole to increase first and then decrease. When the height of the fixed seed position remains unchanged, as the rotation speed of the seed-metering device increases, the qualification rate of the number of holes will also first increase and then decrease. As the rotational speed of the seed-metering device increases, the seed filling time of the hole becomes shorter, and the number of seeds entering the hole will change, resulting in a change in the qualification rate of the number of seeds in the hole [33].

Figure 12b shows the impact of the interaction between the seed-metering device’s rotation speed and the seeding wheel’s aperture on the qualification rate of the number of holes when the seed position height is 120 mm. When the rotational speed of the seed-metering device is fixed, as the hole diameter of the seeding wheel increases, the qualification rate of the number of hole particles gradually decreases and is optimal at 8 mm. When the aperture of the fixed seeding wheel remains unchanged, as the rotational speed of the seed-metering device increases, the number of qualified particles first increases and then decreases. However, overall, it is in a stable state.

Figure 12c shows the impact of the interaction between the seed position height and the seeding wheel aperture on the hole particle number qualification rate when the seed-metering speed is 55 r/min. When the height of the fixed seed position remains unchanged, as the hole diameter of the seeding wheel increases, the qualification rate of the number of holes will gradually decrease. When the aperture of the fixed seeding wheel remains unchanged, as the height of the seed position increases, the number of qualified seeds in the holes first increases and then decreases.

Figure 13a shows the effect of the interaction between the seed-metering speed and the seed height on the seed damage rate when the seed wheel aperture is 8 mm. When the rotation speed of the fixed seed-metering device remains unchanged, as the height of the seed position increases, the seed damage rate gradually increases. When the height of the seed position increases, the pressure on the seeds gradually increases, and the seeds are easily crushed, resulting in a gradual increase in the damage rate of the seeds. When the height of the fixed seed position remains unchanged, as the rotation speed of the seed-metering device increases, the seed damage first decreases and then increases.

Figure 13b shows the effect of the interaction between the seed-metering device speed and the seeding wheel aperture on the seed damage rate when the seed height is 120 mm. When the rotational speed of the fixed seed-metering device remains unchanged, as the hole diameter of the seed-metering wheel increases, the seed damage rate gradually decreases. As the rotational speed of the seed-metering device increases, the seeds are squeezed less and less, thus causing the seed damage rate to decrease gradually. When the aperture of the fixed seeding wheel remains unchanged, as the rotational speed of the seeding device increases, the seed damage first decreases and then increases.

Figure 13c shows the interaction effect between seed height and seeding wheel aperture on the seed damage rate when the seed-metering speed is 55 r/min. When the height of the fixed seed position remains unchanged, as the aperture of the seeding wheel increases, the seed damage rate gradually increases. When the aperture of the fixed seeding wheel remains unchanged, as the height of the seed position increases, the seed damage first decreases and then increases, but overall, it is in a stable state.

3.2.3. Verification Experiment

Use the optimization function in the Design-Expert12 software analysis software to complete the optimization of various parameters of the seed-metering device. When the seed-metering speed is 66.747 r/min, the seed position height is 114.893 mm, and the seeding wheel aperture is 8.075 mm, the operating performance is optimal. At this time, the qualified rate of the number of holes is 91.160%, and the seed damage rate is 0.815%. In order to verify the credibility of the optimization results, with other conditions unchanged, the seed-metering speed was selected to be 67 r/min, the seed position height was 115 mm, and the seeding wheel aperture was 8 mm to conduct three repeated experiments. The average value is calculated as the final experiment result.

The results show that:

• The qualified rate of the number of holes is 90.23%;
• The seed damage rate is 0.62%;
• The error rate of the qualified rate of the number of holes is 1.02%;
• The error rate of the grain damage rate is 23.93%.
• The difference between the actual and optimization results is small, and the optimization results are accurate and credible.

4. Conclusions

According to the agronomic requirements of buckwheat planting, the inner seed-filling hole wheel seed-metering device was designed and completed. The seed discharge port, holes and scraping tongue were analyzed and designed to reduce the leakage and stuck of seeds, and “ one device, two rows “ of seed discharge operation was achieved. The seed-metering device’s rotation speed, seed position’s height, and seed wheel’s aperture were taken as the test factors, and the performance index of the hole seeder, that is, the qualified rate of hole numbers and grain damage rate, were taken as the evaluation criteria, the one-factor test and the response surface test were carried out, and the optimal parameters were verified. The results showed that:

• The degree of influence of various factors on the buckwheat hole sowing seed-metering device from primary to secondary is the seed wheel’s aperture, seed-metering device’s rotation speed, and seed position’s height. The optimal parameter combination of each factor is determined to be the seed-metering device’s rotation speed of 67 r/min, the seed position’s height of 115 mm, and the seed wheel’s aperture of 8 mm.
• Under the optimal parameters, the qualified rate of the number of holes is 90.23%, the grain damage rate is 0.62%, the error rate of the qualified rate of the number of holes is 1.02%, and the grain damage rate is 23.93%. The difference between the actual and optimization results is slight, and the optimization results are accurate and credible.