Design and Test of a Low-Damage Garlic Seeding Device Based on Rigid–Flexible Coupling

Abstract

In conventional mechanized garlic seeding process, seed remains a persistent challenge that is difficult to avoid. This study proposes a solution by designing and testing a garlic seeding device based on a rigid–flexible coupling mechanism, aimed at minimizing seed damage during sowing. The seeding pocket was constructed from a flexible metal sheet, which served as its structural foundation. A slider moving along a fixed track enabled the retraction and release of the pocket, thereby facilitating seed collection and discharge. The effects of pocket radius, rotational speed of seed discharge disc, and thickness of metal sheet on the stress of garlic seeds were investigated through the finite element method. Subsequently, an experimental bench was set up to analyze the effects of influence of these parameters on seed damage rate, single-seed rate, and leakage rate. Results demonstrated that under optimal parameters—a pocket radius of 12 mm, a seed discharge disc rotational speed of 0.21 rad/s, and a metal sheet thickness of 0.15 mm—the mechanism achieved a single-seed rate of 78.4%, a leakage rate of 11.4%, and a maximum stress on garlic seeds of only 0.535 MPa. Notably, this stress level was well below the damage threshold of garlic seeds, resulting in zero damage that outperformed conventional rigid seeding devices. These findings demonstrate the mechanism’s strong potential to preserve seed integrity, although the overall seeding performance remains modest and warrants further optimization in future designs.

1. Introduction

Garlic is a globally important cash crop, with annual production exceeding 28 million tons in China [1,2]. It is valued for its culinary and medicinal properties [3,4,5]. However, mechanized seeding operations are often hindered by high seed damage rates that frequently exceed 12% [6]. This challenge arises from the intrinsic characteristics of garlic cloves, including their irregular geometry, fragile epidermis and variable clove sizes. Mechanical injuries, such as epidermal bruising, internal fractures, or germ damage [7], have been shown to reduce germination rates by 15–30% and decrease yield potential by 6%, thereby constituting a critical bottleneck in the context of sustainable garlic production. Conversely, the enhancement of seeding quality emerges as the most direct and effective technical measure to achieve an increase in the yield per unit area [6,7,8,9]. Hence, the design of the garlic seeding device, which is based on a rigid–flexible coupling, is of great practical significance in reducing damage to garlic seeds during the seeding process.

The primary challenges in precision seeding technology lies in preventing and reducing seed damage. Extensive research has been conducted by numerous scholars on issues related to seed damage in seeding devices. In the field of mechanical seeding device [8], studies have systematically explored three main perspectives: mechanical optimization, material modification, and biomimetic design. Li et al. [9] optimized the angle of the seed wheel (from 15° to 25°) using EDEM simulation, thereby reducing the collision acceleration of corn seeds by 62.5%, lowering the seed damage rate from 8.7% to 2.1%, and increasing the single-seed rate to 96.5%. In the study by Landahl et al. [10], the metal clamping components were substituted with polyurethane elastic finger clamps, which resulted in a 48% reduction in peak contact stress (from 1.8 MPa to 0.94 MPa) and a decrease in soybean seed coat damage rate from 12.3% to 3.8%. Wang et al. [11] developed a speed-adaptive release mechanism based on seed fall trajectory prediction, which increased the rate of seed impact energy absorption by 73%. Furthermore, the rate of rice hull cracking was reduced from 9.2% to 1.7%. Those studies have explored low-damage seeding for specific crops and achieved significant damage reduction effects. However, garlic seeds differ markedly from these crops in terms of morphology, physical properties, and other aspects, and the low-damage seeding technology still requires in-depth exploration. Nevertheless, the aforementioned findings provide highly valuable references for the development of low-damage seeding for garlic seeds.

With regard to garlic seeding, existing research has primarily focused on improving seeding quality, specifically with the core objectives of increasing the single-seed rate and reducing the leakage rate. Ding et al. [12] designed a finger clip plate garlic seeding device that uses a circular truncated cone seed-collecting scoop and splint driven by fine adjustment spring to achieve low-damage seed extraction. Under optimal experimental conditions (finger clip angle of 63°, spoon diameter of 24 mm, and rotation speed of 34 r/min), bench testing showed a single-seed rate of 91.86% and a leakage rate of 2.71%. Hou’s team addressed the technical bottlenecks in single-seed of garlic, successively developing the chain spoon-type [13], wheel spoon-type [14], double charging chamber-type [15], and dragon claw-type seeding devices [16]. However, mechanical hard contact is likely to be injurious to the seed. This is particularly evident in the case of large seeds, such as those of garlic, where the structure of the seed extraction mechanism in the seed box is subject to poor seed’s flow, resulting in the occurrence of friction damage to the garlic seeds. The clamping mechanism results in injury to the garlic seed, attributable to excessive clamping force during the seed-carrying process. However, research on seed damage during garlic sowing is relatively scarce. Zilpilwar et al. [17] developed a cup-feed metering mechanism, achieving a minimal mechanical damage rate of 5.7% in field tests.

Pneumatic seeders employ airflow to adsorb and transport seeds, thereby inherently reducing damage compared with mechanical seeders [18]. Relevant studies have primarily focused on airflow field regulation and changes in adsorption posture [18,19,20], with the core objectives of improving the single-seed rate and reducing the leakage rate. However, these studies have not directly addressed the stress state of seeds during the seeding process and thus cannot quantitatively measure the damage caused to seeds. Meanwhile, the configuration of pneumatic seed extraction structures is complex, requiring auxiliary air pumps and related accessory devices, which leads to increased costs. Furthermore, the force exerted on seeds is positively correlated with both pressure magnitude and aperture size; improper design may still result in damage to seeds.

In this study, a conceptualization of a garlic precision seeding device equipped with a variable diameter track and pocket capture mechanism was proposed. The pocket, constructed from a flexible metal sheet serving as the skeleton and working in tandem with a rigid slider along the fixed track was adopted to achieve retraction and release during the seeding process. The performance of this pocket-based seeding mechanism was analyzed using the finite element method. Furthermore, experimental tests were conducted, and the optimal parameter combination was determined through a second-order orthogonal experimental design.

2. Design of the Seeding Device

2.1. Structure of the Seeding Device

The configuration of the rigid–flexible coupled garlic seeding device is illustrated in Figure 1. The apparatus consisted of a rotating disc, a fixed disc, six sliding bars, six sliders, six seeding pockets, a main shaft, a seed box, a disturbance plate, a camshaft, a cam, and a seed chamber housing. The fixed disc was mounted on the outer housing and featured specific tracks that controlled the reciprocating motion of the sliders. The rotating disc was connected to the main shaft via a hexagonal groove structure at its center. The sliding bars were secured to the rotating disc with screws, and the metal sheets with pockets were fixed to the end of the sliding bars. The disturbance plate was located on the seed chamber housing, at the bottom of the seed box. The cam, positioned below and in contact with the disturbance plate, was connected to the camshaft via a key. The camshaft was connected to the main shaft via a chainwheel. The structural design was analogous to the finger-clip design [12,21], yet it was distinguished by the integration of flexible metal sheets. The flexible metal sheet is composed of steel. The sheet’s thickness ranged from 0.15 mm to 0.25 mm and contributed to its flexibility. This property enabled the sheet to undergo large deformation under external forces and subsequently revert to its original form through the process of elastic recovery once the force was removed. Consequently, it served as one of the control components for the opening and closing mechanism of the pocket.

2.2. Principle of the Seeding Device

The seeding device was divided into three distinct areas, namely the seed collection area, the seed carrying area, and the seed sowing area, based on its operational state (see Figure 2). During the operation, seeds fall from the seed box onto the disturbance plate in the seed collection area. The camshaft then drives the cam to rotate, thereby inducing vibrations in the disturbance plate. These vibrations disperse the garlic seeds within the seed collection area, thereby improving their flowability. The lower ends of the seeds experience both the impact force from the disturbance plate and the gravitational resistance of the seed population, enabling the lower seeds to enter the seeding pockets. Each pocket remains open in this region and rotates with the seed disc, during which it may capture one or two garlic seeds.

Within the designated seed carrying area, the seeding pockets undergo a process of tightening, resulting in the secure enclosure of the garlic seeds. This ensures that the seeds are transported in a stable manner to the designated seed sowing area. The metal sheet’s flexibility ensures that the garlic seed is not damaged during the tightening process, while enhancing both adaptability to garlic seeds and gripping stability. Upon entering the seed sowing area, the sliders retract, causing the pockets to open. Subsequently, the seeds descend under the force of gravity, thereby completing the seeding process.

2.3. Design of Rotating Disc

In order to enhance the seeding stability of the disc, it is necessary to reduce its rotational speed and increase its diameter. In accordance with the rotating disc diameter $d_p$ and the rotational speed n_p, as well as the relationship between the forward speed of the planter $V_c$, the rotating disc diameter was determined to be 200 mm.

An increase in the rotational speed resulted in a corresponding increase in the linear speed of the seeding pockets. This, in turn, reduced the time available for the seed filling, which may have led to unstable capture of the seed. The maximum linear velocity of the seeding pocket was set at 0.35 m/s, and the maximum rotational speed was $n_p$ = 25.9 r/min, according to Equation (1)

$$n_p={\displaystyle \frac{60\times 0.35}{d_p\pi }}$$

(1)

where $d_p$ is the diameter of rotating disc, m; $n_p$ is the rotational speed of rotating disc, r/min.

In order to ascertain the relationship between the spacing of the seeding pockets and the garlic plant spacing, it was necessary to establish the time required for the garlic seeding device to traverse the arc length between the two seeding pockets. This time was equal to the time for the planter to pass through one garlic plant spacing, which was given by:

$$S_p={\displaystyle \frac{S_c{d}_p{n}_p\pi }{(1+\delta )60V_c}}$$

(2)

where $S_p$ is the arc length distance between seeding pockets, m; $V_c$ is the planter speed, m/s; $S_c$ is the garlic plant spacing, m; and $\delta$ is the ground wheel slip coefficient.

Garlic planting agronomic requirements stipulate that the plant spacing $S_c$ should be 80–120 mm, the planter forward speed $V_c$ is between 1–2 km/h, and the ground wheel slip coefficient $\delta$ is between 0.05–0.12. From Equation (2), the arc length between the seeding pockets $S_p$ was 35–112 mm.

According to Equation (3), the number of seeding pockets $n_s$ was in the range of 5 to 17. In this study, the value was set to be 6.

$$n_s={\displaystyle \frac{d_p\pi }{S_p}}$$

(3)

where $n_s$ was the number of seeding pockets.

2.4. Design of the Seeding Pocket

Design of the seeding pocket was optimized in accordance with the dimensions of garlic seeds. A random selection of 300 “Jinxiang” garlic seeds was selected for the purpose of measuring the three-axis dimensions as a benchmark, as shown in Figure 3. It should be noted that the garlic seeds were procured via online retailers and were not subject to any treatment prior to measurement in this section and the bench test in Section 4. The cultivation of “Jinxiang” garlic is a pervasive practice in the Jiangsu region, particularly in the municipality of Jinxiang. This variety is emblematic of the region’s garlic production. The garlic seeds were divided into three levels, the results of which are shown in

Table 1. Three-axis dimensions of garlic seeds.

Grade	Length/mm	Width/mm	Thickness/mm
1	26.5~30.1	13.1~19.8	13.7~16.8
2	29.7~33.2	16~22.5	18.1~21.1
3	32.9~37	19.4~23.7	20.9~22.8

. The specific grading of garlic seed was conducted manually, based on the plumpness of the bulbs. This resulted in an overlapping of data in Table 1.

As illustrated in Figure 4, a volume-variable seeding pocket was designed, with H and R representing the depth and radius of the pocket, respectively. In the seed collection area, each pocket can capture one or two garlic seeds. Through the contraction of the flexible metal sheet, excess seeds with a poor fit are forced to fall away. Therefore, both the radius of the metal sheet (R) and the depth of the seeding pocket (H) play a critical role in the seeding process.

The radius of the metal sheet was selected according to the size distribution of garlic seeds. It was imperative that the diameter of the pocket be larger than the maximum width of the third-grade garlic seeds ($W_{3max}$) and smaller than the minimum length of the first-grade garlic seeds ($L_{1min}$). This was demonstrated in Equation (4). Consequently, the range of metal sheet diameter values ($2R$) was determined to be from 23.7 mm to 26.5 mm. In order to facilitate subsequent analysis, these values were then rounded to 24 mm and 27 mm. Taking into account the uniformity of the data distribution and the precision of the actual sheet radius data production, the radius of the metal sheets ($R$) at the three levels of 12 mm, 12.5 mm and 13 mm was presented.

$$\begin{array}{l}2R<L_{1\min }\\ 2R>W_{3\max }\end{array}$$

(4)

To facilitate the insertion of the garlic seeds into the pocket, the depth of the pocket (H), should be less than the minimum length of the first level of garlic seeds, denoted as $L_{1min}$. Furthermore, to ensure that the gravity center of the garlic seed remains within the pocket, it was essential that the depth of the pocket be bigger than the third level of the maximum length of the garlic seeds ($L_{3max}$), as shown in Equation (5).

$$\begin{array}{l}H<L_{1\min }\\ H>{\displaystyle \frac{L_{3\max }}{2}}\end{array}$$

(5)

According to the size data of garlic seeds, the pocket depth H attained a median value of 22.25 mm within the interval [18.5, 26] and is thus rounded to 22 mm.

2.5. Design of the Retraction Control Mechanism

The fixed disc, slide bar and slider constituted the mechanism that governed the opening and closing of the seeding pocket, and the configuration of the three components is illustrated in Figure 5.

The diameter of the fixed disc was equivalent to that of the rotating disc. The track on the fixed disc was pivotal in controlling the movement of the slider. The slider was equipped with an extended small cylindrical component, measuring 2 mm in diameter and 3 mm in length, which was inserted into the designed track. The width of the track was 2.5 mm, while its depth was 2.2 mm. This ensured that the slider could slide smoothly within the track.

The center of the seeding pocket was positioned at a distance of 21 mm from the end face of the slider bar. Upon entry of the slider into the track with a larger radius, the end face and inner wall of the slider resulted in the metal sheet being compressed, thereby causing the pocket to tighten. Concurrently, the end face of the slider exerted a force on the metal sheet, pushing it to the size of the maximal width of the tertiary garlic seeds, $W_{3max}$. It can thus be deduced that the radius of the large track on the fixed disc should be 21 + 12 − 23.7 ≈ 9 mm larger than the radius of the small track. Therefore, based on the size of the chamber, the radius of the larger track was set to 98 mm, and the radius of the smaller track was set to 89 mm. In order to facilitate the seamless transition of the slider through the arcs, two arcs with a radius of 45 mm were utilized to tangent to the large and small arcs, respectively. The angle of the transition zone is set at 28.5°.

As illustrated in Figure 5c, the distance L between the inner walls on the right side of the slider was pivotal in determining the tightening force of the metal sheet, while the hole (5 mm $\times$ 5 mm) on the other side was for the passage of a rectangle (4.5 mm $\times$ 4 mm) sliding bar. The distances were determined in five levels according to the size of garlic seeds: 6 mm, 6.5 mm, 7 mm, 7.5 mm and 8 mm. A single-factor simulation analysis of the distance L was conducted, with a rotational speed of 0.2 rad/s, a metal sheet thickness of 0.2 mm, and a pocket radius of 12.5 mm utilized. The five stress distributions in garlic seeds were displayed in Figure 6. The detailed simulation settings were described in Section 3.1.

As demonstrated in Figure 6, the maximum stress experienced by garlic seeds is closely related to the distance L, as illustrated in

Table 2. Simulation results of single-factor test.

Inner Wall Spacing/mm	6	6.5	7	7.5	8
Max stress of garlic seed/MPa	4.94	3.66	3.47	2.86	1.48

. The maximum stress experienced by garlic seeds increased with the reduction in L. Previous compression failure tests on garlic seed indicated a critical stress of 3 MPa. It is therefore imperative to obtain a smaller closure size of metal sheet without damaging the garlic seeds. The distance was taken to be 7.5 mm.

3. Simulation of the Seeding Process

3.1. Simulation Model Establishment

The focus of this simulation (conducted in Abaqus 2020) entailed the entire process of seed picking, seed carrying, and seed dropping by the seeding pocket through the opening and closing of the metal sheet. The structures except for the seeding pocket, garlic and the metal sheet were set as rigid bodies. The explicit dynamics analysis of finite element method was utilized to simulate the interaction between the metal sheet- pocket-garlic seed. The relevant material parameters are presented in

Table 3. Material parameters.

Material	Modulus of Elasticity/MPa	Poisson’s Ratio	Density/t/mm3
Garlic seed	23.82	0.25 [22]	5.1 × 10−9
Metal sheet	210,000	0.3	7.8 × 10−9
Seeding Pocket [23] (cotton fabric)	9.15	0.142	1.5 × 10−9

. It is important to note that, due to its flexible nature, the seeding pocket served only to hold the garlic seeds in place, and its material parameters did not significantly affect the simulation results.

In order to reduce the computational burden, the fixed disk with tracks retained only its track characteristics, as illustrated in Figure 7, where “×” stands for the rotation center. The trajectory of the slider end as it moved along the track on the fixed disc was established by the one-dimensional rigid lines. Furthermore, the seeding pocket was modelled using two-dimensional membrane elements, incorporating a total of 1389 M3D4R elements and 6 M3D3 elements. The garlic seeds were modelled with three-dimensional solid elements, consisting of 189 C3D8R elements and 269 C3D4 elements. The metal sheet was modelled using beam elements, with a total of 112 B31 elements.

In the context of the simulations, the dynamic explicit step was utilized, and a mass scaling was implemented, which resulted in a reduction in computation time. It was imperative to implement a step with ramp load in order to mitigate the consequences of mass scaling, which had the potential to induce excessive inertia. Over a period of one second, the system gradually accelerated from 0 to three levels: 0.15 rad/s, 0.2 rad/s, and 0.25 rad/s, respectively. In the subsequent step, the system underwent rotation at a constant speed of 0.15 rad/s, 0.2 rad/s, and 0.25 rad/s, respectively. Simulation tests showed that the mass scaling setting of 10⁻⁶ s did not have a significant impact on the results.

3.2. Simulation Process of the Seeding

In the seed-collecting process, as the track radius gradually increased, the slider moved outward, and the metal sheet tightened the pocket, as seen in Figure 8a. Meanwhile, the stress curve fluctuated and gradually rose with the step time. In the seed-carrying process, the garlic seeds remained firmly fixed, and the internal stress oscillated slightly, as seen in Figure 8b. In the seed-sowing process, the track radius gradually decreased, the slider retreated, and the metal sheet recovered under the elastic action to open the pocket, which caused the internal stress of the garlic seed to gradually decrease, as seen in Figure 8c. Finally, the garlic seed became separated from the pocket due to its gravity and centrifugal force, completing the seeding process. The stress experienced at the critical point of the garlic seed during the seeding process can be seen in Figure 8d.

3.3. Multifactorial Analysis of Damage to Garlic Seed

In order to investigate the damage of garlic seeds during the seeding process, the radius of the pocket (x₁), the rotational speed of the seeding disc (x₂) and the thickness of the metal sheet (x₃) were selected as the experimental variables according to the designed structure, the maximum stress on garlic seed during the seeding process was used as an evaluation index $Y_1$. The experimental factors and codes are shown in

Table 4. Test factors and codes.

Code	Factors
	Pocket Radius ${\mathit{x}}_1$/mm	Rotational Speeds of Seeding Disc ${\mathit{x}}_2$/rad/s	Thickness of Metal Sheet ${\mathit{x}}_3$/mm
−1	12	0.15	0.15
0	12.5	0.2	0.2
1	13	0.25	0.25

. X₁, X₂, and X₃ are coded values for the test factors. The test program and the results are shown in

Table 5. Test protocol and results for garlic seeds.

No.	Factors			Y1/MPa
	${\mathit{X}}_1$	${\mathit{X}}_2$	${\mathit{X}}_3$
1	−1	−1	0	1.99
2	1	−1	0	1.31
3	−1	1	0	0.77
4	1	1	0	0.91
5	−1	0	−1	0.603
6	1	0	−1	0.428
7	−1	0	1	0.84
8	1	0	1	0.684
9	0	−1	−1	2.03
10	0	1	−1	1.31
11	0	−1	1	2.03
12	0	1	1	2.17
13	0	0	0	2.55
14	0	0	0	2.86
15	0	0	0	2.73
16	0	0	0	2.57
17	0	0	0	2.37

.

As illustrated in Figure 9, the Mises equivalent stress (S) distribution of garlic seeds under pocket closing conditions was investigated in the 17 simulations, according to Table 5. The action of the metal sheet was the primary source of stress on the garlic seed. Consequently, the garlic seed experienced the greatest level of stress in contact with the metal sheet, as illustrated in the red section of the figure. Previous compression failure tests on garlic seeds indicated that its critical stress for damage was approximately 3 MPa. While the maximum stress received by the garlic seeds in all 17 analyses was found not to exceed 3 MPa, indicating that the rigid–flexible coupling of garlic seed tray can significantly reduce the damage of garlic.

The utilization of Design-Expert 13 software to conduct an analysis of variance on the garlic stress data presented in Table 5 yielded the results displayed in

Table 6. Variance analysis of garlic stress.

Source of Variance	Garlic Stress ${\mathit{Y}}_1$
	Sum of Squares	Degree of Freedom	F	p
Model	10.91	9	28.58	0.0001
$x_1$	0.0948	1	2.23	0.1786
$x_2$	0.6050	1	14.26	0.0069
$x_3$	0.2288	1	5.39	0.0532
$x_1{x}_2$	0.1681	1	3.96	0.0868
$x_1{x}_3$	0.0001	1	0.0021	0.9645
$x_2{x}_3$	0.1849	1	4.36	0.0752
$x_1^2$	7.21	1	169.94	<0.0001
$x_2^2$	0.0164	1	0.3861	0.5541
$x_3^2$	1.88	1	44.36	0.0003
Residual	0.2970	7
Lack of Fit	0.1575	3	1.51	0.3418
Pure error	0.1395	4
Cor Total	11.21	16

. The p-value of the maximum stress regression model was less than 0.01, which was highly significant. In contrast, the p-value of the lack of fit was greater than 0.05, thereby indicating that lack of fit was not significant. A thorough examination of the p-value indicated that within the maximum stress regression model, $x_2$, $x_1^2$ and $x_3^2$ exerted a profoundly significant influence on the model. The relative importance of these three factors in determining the impact of maximum stress on garlic seeds was determined by the rotational speed of the disc, the thickness of the sheet, and the radius of the pocket. Multiple linear regression analysis was conducted on the experimental results, and the multiple regression equation for the maximum stress of garlic seeds was obtained:

$$\begin{array}{ll}{Y}_1& =2.62-0.11x_1-0.28x_2+0.17x_3+0.21x_1{x}_2\\ & + 0.22x_2{x}_3-1.31x_1^2-0.06x_2^2-0.67x_3^2\end{array}$$

(6)

The interaction between the two factors on the evaluation index was analyzed, respectively, with the remaining factors taken as middle values, as demonstrated in Figure 10.

As illustrated in Figure 10a, the interaction between the radius of the pocket and the rotational speed of the disc exerted a significant influence on the maximum stress of garlic seed during the seed picking process, under conditions where the thickness of the metal sheet was maintained at X₃ = 0. When the rotational speed is constant, a small pocket radius fails to fully grasp the garlic clove, resulting in the ineffective exertion of the force from the metal sheet. As the radius increases, the metal sheet can completely and firmly grip the garlic clove, causing the stress on the clove to reach its maximum value. With a continuous increase in radius, the pocket becomes loose and fails to form an effective fixation on the garlic clove, leading to a reduction in the clove’s stress. Therefore, the stress on the garlic clove first increases and then decreases with the increase in radius. When the pocket radius is constant, an increase in rotational speed enhances the centrifugal force acting on the garlic clove, making it easier for the clove to fully enter the pocket. This causes the metal sheet to encircle the clove at a position outside its maximum dimension, thereby reducing the stress on the garlic clove.

As illustrated in Figure 10b, the maximum stress demonstrated a tendency to increase, followed by a subsequent decrease, in accordance with the augmentation of the pocket radius or the thickness of the metal sheet. As stated above, the influence of the pocket radius on the maximum stress is mainly caused by the position where the metal sheet acts on the garlic clove. Regarding the thickness of the metal sheet: when the metal sheet is relatively thin, the hole formed after deformation presents a long and narrow shape; however, its good flexibility helps reduce the stress on the garlic clove. When the metal wire is thicker, the width and narrowness of the deformed hole are relatively similar, so it will not clamp the garlic clove too tightly, thereby reducing the stress on the clove.

As illustrated in Figure 10c, the interaction between the rotational speed and the thickness of the metal sheet exerted a significant influence on the maximum stress. The influence of metal sheet thickness on the maximum stress of garlic seeds mainly stems from its flexibility and the morphology after deformation, whereas the influence of rotational speed on the maximum stress of garlic seeds is primarily attributed to inertial force.

4. Bench Test

4.1. Test Preparation

A test bench for the performance of the seeding device was constructed, as illustrated in Figure 11. The fixed disc, rotating disc, sliding bar and slider were manufactured using a 3D printer. Regarding the style of basketball bag, six pockets were created by wrapping six metal sheets with fabric. The driving motor of the rotating disc was selected as PFDE 7IK40CRGU-CF (China), with a rated power of 400 W. Furthermore, the model of the motor driving the seed disturbance plate was identified as WUP M425-402 (China). According to GB/T 6973-2005, entitled “Testing methods of single seed drills (precision drills)” [24], the number of seeds recorded as the statistical object during the operation of the seeding device when it is functioning at a constant value was 251. Each experiment was replicated five times, and the mean value was calculated.

Around 400 garlic seeds were deposited into the designated seed box, after which the motor was activated. The rotation of the rotating disc was initiated, and the disturbance plate commenced oscillation. The seeding pockets located on the rotating disc passed upwards through the seed box, captured a garlic seed, and commenced tightening. The seed was then transported to the designated seed sowing area, where it underwent a process of opening of the seeding pockets. The garlic seed then fell into the collection box under the action of gravity.

The present experiment was centered on the investigation of damage to garlic seeds, with the primary objective being the collection of data on garlic seed damage. Concurrently, the single-seed rate and leakage rate were also recorded. The collection of data pertaining to damage rate $Y_2$, the single-seed rate $Y_3$, and the leakage rate $Y_4$ was derived using Equations (7)–(9).

$$Y_2={\displaystyle \frac{N_{\mathit{damage}}}{N_{\mathit{total}}}}\times 100\%$$

(7)

$$Y_3={\displaystyle \frac{N_{\mathit{single}}}{N_{\mathit{total}}}}\times 100\%$$

(8)

$$Y_4={\displaystyle \frac{N_{\mathit{leakage}}}{N_{\mathit{total}}}}\times 100\%$$

(9)

where $N_{\mathit{damage}}$, $N_{\mathit{single}}$, $N_{\mathit{leakage}}$ and $N_{\mathit{total}}$ are the numbers of damage seed, single seed, leakage seed, and the total seed, respectively.

4.2. Analysis of Test Results

The multi-factor test was conducted, with the damage rate ($Y_2$), single-seed rate ($Y_3$) and the seed leakage rate ($Y_4$) as the evaluations and the factor coding values ($x_1$, $x_2$ and $x_3$). The test results are presented in

Table 7. Bench test results.

No.	Factors			Performance Indexes
	X1	X2	X3	Damage Rate ${\mathit{Y}}_2$/%	Single Seed Rate ${\mathit{Y}}_3$/%	Leakage Rate ${\mathit{Y}}_4$/%
1	0	0	0	0	74.8	13.6
2	1	0	−1	0	72.9	14.6
3	0	0	0	0	73.9	14.1
4	1	1	0	0	68.6	16.9
5	1	0	1	0	72.8	14.7
6	−1	−1	0	0	70.0	16.1
7	0	0	0	0	75.5	13.2
8	0	−1	−1	0	73.0	15.3
9	−1	0	−1	0	79.1	11.4
10	1	−1	0	0	68.8	16.8
11	0	1	1	0	75.0	13.5
12	0	0	0	0	76.5	12.8
13	0	1	−1	0	72.5	14.8
14	0	0	0	0	77.2	12.4
15	−1	0	1	0	76.2	15.1
16	0	−1	1	0	66.9	17.8
17	−1	1	0	0	71.9	12.9

. Given that the damage rate $Y_2$ was zero, it was determined that further analysis was not required.

ANOVA was performed on the damage rate, single-seed rate and leakage rate, as shown in

Table 8. Variance analysis for bench tests.

Source of Variance	Single Seed Rate ${\mathit{Y}}_3$				Leakage Rate ${\mathit{Y}}_4$
	Sum of Squares	Degree of Freedom	F	p	Sum of Squares	Degree of Freedom	F	p
Model	161.33	9	8.91	0.0044	45.33	9	10.29	0.0028
$X_1$	24.64	1	12.24	0.0100	7.03	1	14.37	0.0068
$X_2$	11.03	1	5.48	0.0518	7.80	1	15.94	0.0052
$X_3$	5.55	1	2.76	0.1406	3.12	1	6.39	0.0394
$X_1{X}_2$	1.12	1	0.5589	0.4791	2.72	1	5.56	0.0504
$X_1{X}_3$	2.00	1	0.9935	0.3521	3.24	1	6.62	0.0368
$X_2{X}_3$	18.86	1	9.37	0.0183	3.61	1	7.38	0.0299
$X_1^2$	6.01	1	2.98	0.1277	1.17	1	2.39	0.1657
$X_2^2$	88.24	1	43.85	0.0003	15.64	1	31.97	0.0008
$X_3^2$	3.05	1	1.51	0.2581	0.1727	1	0.3528	0.5712
Residual	14.09	7			3.43	7
Lack of Fit	7.55	3	1.54	0.3349	1.66	3	1.25	0.4028
Pure error	6.54	4			1.77	4
Cor Total	175.42	16			48.76	16

, using Design-Expert 13 software. The p-values of the two regression models were less than 0.01, which was highly significant. However, the p-values of the lack of fit were greater than 0.05, indicating that the lack of fit was not significant. A thorough examination of the p-value revealed that, within the single seed rate regression model, both $x_1$ and $x_2^2$ exhibited a significant impact on the model, while $x_2{x}_3$ demonstrated a significant effect. The three factors affecting the single seed rate were the pocket radius, the rotational speed, and the thickness of the metal sheet, in that order of importance. In the leakage rate regression model, $x_1$, $x_2$, $x_2^2$ exhibited a highly significant effect on the model, while $x_3$, $x_1{x}_3$, $x_2{x}_3$ demonstrated a significant effect. The three factors affecting the seed leakage rate were the rotational speed, the pocket radius, and the thickness of the metal sheet, in order of importance. Multiple linear regression was fitted to the experimental results to obtain the multiple regression equations for single-seed rate $Y_3$ and seed leakage rate $Y_4$ (Equation (10)).

$$\begin{array}{ll}{Y}_3& =75.6-1.8x_1+1.2x_2-0.8x_3-0.5x_1{x}_2+0.7x_1{x}_3\\ & + 2.2x_2{x}_3-1.2x_1^2-4.6x_2^2+0.9x_3^2\\ Y_4& =13.2+0.9x_1-1.0x_2+0.6x_3+0.8x_1{x}_2-0.9x_1{x}_3\\ & -1.0x_2{x}_3+0.5x_1^2+1.9x_2^2+0.2x_3^2\end{array}$$

(10)

As illustrated in Figure 12, the response surface for the single seed rate $Y_3$ was depicted. In Figure 12a, the interaction between the pocket radius and the rotational speed of the seed-picking disc exerted a significant influence on the single seed rate, with the thickness of the metal sheet fixed at an intermediate level. When the rotational speed is constant, an increase in the pocket radius leads to an expansion of the opening area of the metal sheet, which in turn affects the single-seed rate. When the pocket radius is constant, an excessively low rotational speed prolongs the seed-picking time and increases the interaction duration between garlic cloves, which is unfavorable for stably picking up the cloves. In contrast, an excessively high rotational speed also impairs the stability of seed picking.

As illustrated in Figure 12b, the interaction between the pocket radius and the thickness of the metal sheet exerted a significant influence on the single seed rate when the rotational speed was set to an intermediate level. As mentioned above, the influence of the pocket radius on the single-seed rate is mainly associated with the opening area of the metal sheet. When the pocket radius is constant, with an increase in the thickness of the metal sheet, the hole formed after its deformation not only becomes closer to a circular shape but also has a larger opening area. This allows garlic cloves in any posture to enter, thereby exerting an influence on the single-seed rate.

As illustrated in Figure 12c, the interaction between the rotation speed and the thickness of the metal sheet exerts a significant influence on the single seed rate, under the condition that the radius of the pocket was designated as the midpoint. At low rotational speeds, the seed-picking duration is relatively long. As the thickness of the metal sheet increases, the opening area of the deformed sheet becomes larger, making it easier for garlic cloves in any posture to enter—this leads to a decrease in the single-seed rate. While at high rotational speeds, although the deformed thick metal sheet also has a large opening area, the interaction duration is short; additionally, the effect of inertial force is prominent. As a result, some garlic cloves with unstable positioning are thrown out, which contributes to an increase in the single-seed rate.

As shown in Figure 13, the response surface for the seed leakage rate $Y_4$ was presented. In Figure 13a, the interaction between the pocket radius and the rotational speed of the seed-picking disc exerted a significant influence on the seed leakage rate, with the thickness of the metal sheet fixed at an intermediate level. Under low rotational speed conditions, the seed-picking duration is relatively long: an excessively small pocket radius is unfavorable for the entry of garlic cloves, while an excessively large pocket radius may cause multiple garlic cloves to get stuck at the entrance of the pocket. Under high rotational speed conditions, the effect of inertial force is significant. As the pocket radius increases, more garlic cloves are disturbed and collide with each other, which may be unfavorable for their entry into the pocket. When the pocket radius is small, an increase in rotational speed makes it easier for garlic cloves to enter the pocket under the action of inertial force, thereby reducing the seed leakage rate. And when the pocket radius is large, an excessively low rotational speed causes multiple garlic cloves to get stuck at the pocket entrance, while an excessively high rotational speed leads to increased collisions between garlic cloves—both scenarios result in an increase in the seed leakage rate.

As illustrated in Figure 13b, the interaction between pocket radius and metal sheet thickness exerted a significant influence on the rate of seed leakage, under conditions wherein the rotational speed was maintained at an intermediate level. Regardless of the thickness of the metal sheet, an excessively large pocket radius will lead to increased seed leakage rate. This is because as the size of the pocket increases, its flexibility becomes uncontrollable, resulting in torsional deformation. When the metal sheet is relatively thick, an excessively small pocket radius is unfavorable for the entry of garlic cloves. In contrast, when the metal sheet is relatively thin, its good flexibility allows garlic cloves to squeeze into the pocket. Under the condition of a large pocket radius, an increase in the thickness of the metal sheet reduces its flexibility and enhances the stability of the opening shape, which facilitates the entry of garlic cloves and thus decreases the seed leakage rate. Under the condition of a small pocket radius, an increase in the thickness of the metal sheet reduces the opening area, which is unfavorable for the entry of garlic cloves and consequently increases the seed leakage rate.

From Figure 13c, the interaction between the rotational speed and the thickness of the metal sheet had a significant impact on the seed leakage rate, when the pocket radius was maintained at an intermediate level. Under low rotational speed conditions, an increase in the thickness of the metal sheet reduces the opening area to a certain extent, which impairs the entry of garlic cloves. While under high rotational speed conditions, due to the significant effect of inertial force, garlic cloves can be squeezed into the pocket. When the thickness of the metal sheet is constant, an excessively low rotational speed prolongs the seed-picking time and increases collisions between garlic cloves. In contrast, an excessively high rotational speed causes excessive disturbance to the garlic cloves, resulting in their instability—both scenarios are unfavorable for seed picking.

A comparison of Figure 12 and Figure 13 revealed that the influence of each factor on the single-seed rate and seed leakage rate was relatively similar. In fact, these two sets of data were inherently related–an increase in the single-seed rate inevitably led to a decrease in the seed leakage rate. This confirmed the reliability of the analysis process.

The following conditions (Equation (11)) were employed to ascertain the level combinations that would result in the single-seed rate attaining its maximum value, the seed leakage rate attaining its minimum value, and the maximum stress of garlic seed falling below the limit value, utilizing the optimization function of the software.

$$\left\{\begin{array}{c}0<Y_1<3\\ \max Y_3\\ \min Y_4\\ s.t.\left\{\begin{array}{c}-1\le X_1\le 1\\ -1\le X_2\le 1\\ -1\le X_3\le 1\end{array}\right.\end{array}\right.$$

(11)

Following a thorough analysis of the optimal working parameters, the following conclusions were reached: the radius of the pocket was established at 12 mm, the rotational speed of the seed-picking disc was set at 0.21 rad/s, and the thickness of the metal sheet was determined to be 0.15 mm. In the context of this specific combination, the model predicts that the single-seed rate was 78.4%, the seed leakage rate was 11.4%, and the maximum stress experienced by the garlic seed was 0.535 MPa.

Bench tests using the optimal combination of parameters revealed that zero damage to the garlic seed was achieved despite the lower single grain rate. Compared with spoon-chain and finger-clamp types, this device’s sowing quality, such as single-seed rate and leakage rate, is not ideal. However, simulations and experiments have proven that the device can sow garlic seeds without causing any damage. Further optimization could target the single-seed rate and leakage rate to improve sowing quality.

5. Conclusions

The problem of high damage rate of garlic seeds in traditional seeding devices has been identified as a key issue requiring investigation. To address this, a new garlic seeding device with a rigid–flexible coupling mechanism was designed, and its key structural parameters were determined through theoretical analysis, simulation, and experimental testing. The primary conclusions are as follow:

• Orthogonal simulation tests were conducted to evaluate the effects of different conditions on garlic seed stress. The results showed that under an inner wall spacing of 7.5 mm, the stress levels of all 17 garlic seeds remained below 3 MPa, confirming that this design can effectively reduce seed damage.
• Using the Box–Behnken experimental design, a three-factor, three-level regression orthogonal test was performed. The results demonstrated that the optimal seeding performance was achieved with a pocket radius of 12 mm, a rotational speed of 0.21 rad/s, and a metal sheet thickness of 0.15 mm. Under these conditions, the device achieved a single-seed rate of 78.4%, a leakage rate of 11.4%, and a maximum seed stress of only 0.535 MPa.