Design and Experiments of a Planting Mechanism for Chuanxiong Seed Stalk Cuttage

Abstract

To address the challenges of the lack of specialized machinery adapted to traditional agronomic requirements, high labor intensity, and low efficiency in the planting of Ligusticum chuanxiong stalk segments (commonly known as Chuanxiong seed stalk or Lingzhong), a planting mechanism for the cutting of Chuanxiong seed stalk was developed in accordance with traditional agronomic requirements. A kinematic model of the gripping point was established, from which a plant spacing formula was derived. Based on the zero-speed planting principle, a cuttage planting scheme for Chuanxiong seed stalks was proposed, in which the gripper trajectory as well as the forward-tilt x_t and correction x_c were defined, and the decisive role of installation height on planting depth and the influence of driven-sprocket motion parameters on planting uprightness were elucidated. A 3D model and a DEM-MBD coupled simulation model were constructed to analyze planter–soil–seed interaction. A three-factor, three-level Box–Behnken experiment was conducted, and a response surface model was built and optimized using ‘Design-Expert’ software. The optimal parameters were a driven sprocket angular velocity of 0.654 rad/s, a rotation radius of 100.787 mm, and a release angle of 90.647°, yielding an average planting uprightness of 85.264°, with the corresponding x_t and x_c of 5.18 mm and 2.69 mm, respectively; the factor influence ranked as angular velocity > rotation radius > release angle. Seed–soil interaction analysis verified the mechanism’s feasibility and the accuracy of the theoretical models. Field tests showed average qualification rates of 87.13% for plant spacing, 96.01% for planting depth, and 90.41% for uprightness, with corresponding coefficients of variation of 4.37%, 2.95%, and 3.73%, indicating stable and reliable field performance.

1. Introduction

Ligusticum chuanxiong is one of the most widely cultivated authentic Chinese medicinal herbs in Sichuan Province [1,2]. It has high medicinal value. Chuanxiong seed stalks have strict agronomic requirements: improper planting depth reduces seedling emergence, whereas the optimal depth ensures that the node disc makes proper contact with the soil. After planting, the bud on the Chuanxiong node disc should face upward. Therefore, the planting hole should be as small as possible to prevent lodging. Traditionally, the Chuanxiong seed stalk is planted in large ridges with five rows. Currently, Chuanxiong seed stalks are mainly planted manually by plug-in insertion. This method is labor-intensive and inefficient. To reduce labor costs, some regions use furrow sowing. However, furrow sowing does not follow traditional insertion-based agronomic practices. It cannot ensure that the seed stalks remain upright after planting or that the buds face upward. These strict agronomic requirements, combined with the irregular shape of the seed stalks, hinder the development of mechanized planting equipment. As a result, the mechanization level of the planting process remains low [3,4,5].

The planting mechanism is the core component of a planting machine. It includes the planting device, which inserts the planting object into the soil. The mechanism drives the planting device to complete a series of planting actions. Many researchers have conducted in-depth studies on planting mechanisms [6,7,8,9]. Ali et al. designed a link-type duckbill transplanter for plug seedlings and optimized the motion trajectory to reduce soil disturbance. A four-bar linkage mechanism with optimized link lengths (driving link 50 mm, connecting link 120 mm, guide bar 120 mm, end-effector 220 mm, dibbling hopper 153 mm) was validated via kinematic simulation and bench tests. The mechanism achieved end-effector velocities of 284 mm/s and 1379 mm/s in the X and Y directions, accelerations of 1241 mm/s² and 8664 mm/s², driving power of 17.4 W, and improved seedling uprightness, demonstrating effective planting performance with minimal soil disturbance [10]. Shi et al. optimized the duckbill transplanter for multi-row vegetable seedlings to reduce soil resistance. DEM–MBD simulation and response surface analysis identified the optimal end-effector shape. Field tests showed a planting qualification rate of 96.62%, spacing CV of 3.55%, and efficiency of 7135 plants/h, confirming the mechanism’s feasibility [11]. Sharma et al. developed a semi-automatic, two-row tractor-mounted vegetable plug seedling transplanter, featuring a 5-bar planting mechanism, a hopping dibber, and a half-open double-door soil-covering unit. The design, kinematic analysis, and preliminary laboratory and field tests were conducted to evaluate functional viability and the effects of tray cavity type, feeding system, soil-covering wheel angle, and seedling age on transplanting performance, achieving upright plant rates of 89–95% and a planting geometry of 0.60 × 0.45 m [12]. Hwang S.-J. et al. analyzed the trajectory of a semi-automatic vegetable transplanter using kinematic simulation software and high-speed cameras. They optimized the lengths of the linkage mechanism while maintaining the desired trajectory. This reduced both manufacturing and fuel costs [13]. Wang et al. designed a non-circular gear–linkage combination planetary transplanting mechanism, including a five-bar seedling pushing mechanism and a cam-linkage supporting mechanism. The kinematic model and virtual simulation were used to optimize the motion trajectory and key parameters. Prototype tests showed that when the mechanism operated at 60–80 r/min, the transplanting success rate of broccoli and pepper seedlings exceeded 93%, indicating effective seedling protection and practical applicability [14]. Khadatkar et al. developed an automatic vegetable transplanter for chili plug seedlings, featuring a rotating-finger device with a push-type mechanism. The system includes L-shaped fingers, a feed roller, a metering unit, and a delivery unit. Tests showed plant spacing of 599.8 mm, planting depth of 46.4 mm, mis-planting 4.9%, multiple planting 1.1%, seedling mortality 0.9%, transplanting success 92.6%, field efficiency 76.12%, and effective field capacity 0.093 ha/h, outperforming manual planting (0.027 ha/h) [15].

In addition, the interaction among soil, plant, and machine during the planting process also affects planting performance. Many researchers have conducted in-depth studies on soil–plant–machine interaction [16,17]. Quan et al. aimed to address the mismatch between the theoretical and actual hole dimensions in a rapeseed transplanting device. They established a kinematic model of the hole-forming device during the planting process. Bench tests were conducted to determine the optimal forward speed for forming stable holes. The results improved the qualification rate and stability of hole formation [18]. Yang et al. investigated the dynamic hole-forming performance of a cup-hanging planter using DEM-MBD coupling simulation. The study revealed that different cup shapes significantly affect soil action mechanisms and hole-forming performance. Specifically, the conical hanging cup produced smaller longitudinal hole dimensions and better film-tearing performance compared to the multilateral cup, while both met the planting depth requirements. The validation through bench tests confirmed that DEM-MBD coupling simulation can reliably predict the hole-forming characteristics of cup-hanging planters [19]. Chen et al. optimized the hole-forming device of a buckwheat hole seeder using DEM-MBD co-simulation. Based on simulation results, the opening and closing spring type was selected according to hole quality. A single-factor experiment was conducted on the rotation speed of the device. A reasonable speed range was identified, which improved the seeding qualification rate of the buckwheat hole seeder [20].

In summary, existing studies mainly focus on the design and optimization of planting mechanisms for plug seedlings and potted seedlings. These mechanisms typically form holes by driving mechanical components into the soil. However, traditional cultivation of Ligusticum chuanxiong involves directly inserting Chuanxiong seed stalks into the soil. This process is governed by the coupled interaction among soil, seed stalk, and planting mechanism, rather than by soil opening alone. Few studies have developed planting mechanisms or new types of planters specifically for the mechanized planting of cuttings while considering this soil–plant–machine interaction framework.

To realize the mechanized planting of Chuanxiong seed stalks and to meet the agronomic requirements of traditional insertion-based cultivation regarding the post-planting posture of the Chuanxiong seed stalks, this study proposes an innovative insertion-type planting mechanism. The mechanism grips the Chuanxiong seed stalk and inserts it directly into the soil. It features a compact structure, stable operation, and the ability to mount multiple planting devices for high-efficiency planting. From the perspective of soil–plant–machine interaction, a theoretical analysis and kinematic model of the planting mechanism were established. Based on the traditional agronomic requirements for planting spacing and depth of Chuanxiong seed stalks, and their interaction with soil during insertion, the effects of three key parameters on planting uprightness were studied: the angular velocity of the driven sprocket, its rotation radius, and the sprocket rotation angle at the moment of seed release. The acceptable ranges for these parameters were preliminarily determined. The DEM-MBD co-simulation was then used to optimize these parameters through regression experiments. Through this coupled soil–seed stalk–machine model, the key structural parameters of the cuttage planting mechanism were designed. Further analysis was conducted to investigate the interaction between the planter, Lingzhong, and soil, and to validate the theoretical planting mechanism of Lingzhong. A prototype was developed and field-tested to evaluate its performance. By integrating soil, plant, and machine interactions into the design and optimization process, this study provides a reference for the development of mechanized planting mechanisms for cuttage-planted crops.

2. Materials and Methods

2.1. Structure and Working Principle of the Planting Mechanism

The cuttage planting mechanism for Chuanxiong seed stalks consists of driving sprocket, planter, seed preparation platform, opener, connecting rod, driven sprocket, hinged support, support frame, and chain. The connecting rod connects two chains via the hinged support, and the planter is installed at the end of the connecting rod. Multiple planters are evenly arranged along the chain assembly. Both the driving sprocket and the driven sprocket have 40 teeth and are matched with an 08A roller chain. As the driving sprocket rotates, the planters move with the chains, completing the processes of seed picking, transporting, and planting, as shown in Figure 1.

The driven sprocket and chain assembly constitute the key motion transmission components of the planting mechanism. The rotational motion of the driven sprocket directly determines the movement trajectory of the planter during the planting process. Therefore, the angular velocity and rotational radius of the driven sprocket, as well as the release position of the planter, are identified as the key technical characteristics affecting planting performance. These parameters are derived from the structural design of the prototype and provide the physical basis for the subsequent kinematic modeling and optimization.

During operation, the planter moves with the chain. Under the control of the connecting rod, the opening of planter remains vertically downward. The Chuanxiong seed stalks are placed on the seed preparation platform. As the planter passes over the seed preparation platform, it grips a Chuanxiong seed stalk. Driven by the transmission chain, the planter transports the Chuanxiong seed stalk to the planting position. The planter then inserts the Chuanxiong seed stalk into the soil. With the help of the opener, the planter releases the Chuanxiong seed stalk. After leaving the opener, the planter returns to the seed-picking position. The planting mechanism operates in a continuous cycle.

The function of the planting mechanism is to plant Chuanxiong seed stalks into the soil under agronomic requirements. Therefore, the designed mechanism must complete a series of complex tasks, including Seed taking, conveying, planting, releasing, and returning, through a specific motion path. The detailed design requirements are as follows: (a) The mechanism must meet the agronomic requirements of Chuanxiong planting. The traditional agronomic method is insertion planting. The Chuanxiong seed stalk should be inserted to a depth of 30 mm, and parameters of planting density are the row spacing of 250 mm and the planting spacing of 180~200 mm. (b) The motion path of the planter must ensure planting stability. To reduce lodging after planting, the hole opening width should be minimized to keep the rhizome upright. The Chuanxiong seed stalk should enter the soil smoothly. The desired motion path should approximate a curtate cycloid to achieve zero-speed planting [21,22], as shown in Figure 2.

The Chuanxiong seed stalks are prepared by cutting off the stalks at both ends of the nodes. The stalk at the end without a bud is trimmed to approximately 30 mm. During planting, the node disc should fully contact the soil, but the soil should not completely cover the seed stalk, achieving an optimal planting depth of about 30 mm. The planting spacing is controlled at 180~200 mm, and the bud eye should face upward. The vertical orientation of the seed stalk is ensured by designing the motion trajectory of the planting mechanism and controlling the timing of seed entry and release points. The above agronomic requirements for Chuanxiong seed stalk planting will be realized through the design of the planting mechanism and optimization of key parameters.

2.2. Analysis of the Planting Trajectory

In Figure 3, the motion of the planter is the combined trajectory of its movement around the transmission chain and the forward movement of the machine. The planting point Z is defined as the position of the gripping point T when the seed stalk first contacts the soil. The release point S is the position of point T when the planter reaches the lowest point of the working trajectory. To ensure smooth insertion of the Chuanxiong seed stalk and meet the planting depth requirement while minimizing the hole width, two conditions must be satisfied. First, the absolute horizontal displacement between points Z and S should approach zero. Second, the absolute vertical displacement between points Z and S should approach the planting depth.

A Cartesian coordinate system xOy is established for the motion of the planting mechanism, as shown in Figure 3. The positive x-axis is aligned with the forward direction of the machine, and the positive y-axis points vertically upward from the ground surface. The origin O is located at the center of the driven sprocket.

To simplify the kinematic analysis, the following assumptions were adopted:

(1)

The chain transmission was assumed to be rigid, and the effects of chain elasticity were neglected, since the chain used in the mechanism has high stiffness.

(2)

The hinged joints between the hinged support and the connecting rod were assembled using an interference fit between shafts and bearings; therefore, joint clearances and backlash were neglected.

(3)

All components were considered as rigid bodies, and the motion of the planting mechanism was assumed to be planar.

(4)

Soil reaction forces were not considered during the derivation of the gripping point trajectory. This is because the soil was sufficiently tilled to obtain a relatively uniform and leveled surface before planting, and the insertion resistance mainly affects the planting force rather than the kinematic trajectory.

During the Chuanxiong seed stalk planting stage, the planter’s gripping point T moves along arc AB. Taking point A as the initial position and point B as the final position, the relative displacement equation of the gripping point T during this interval is expressed as:

$$\left\{\begin{array}{l}x={\displaystyle \frac{\theta V}{w}}+(R+h_1)\cos \theta \\ y=-d-h_2-(R+h_1)\sin \theta \end{array}\right. (0\le \theta <\pi )$$

(1)

where x is the horizontal displacement of the gripping point T (mm); y is the vertical displacement of the gripping point T (mm); θ is the rotation angle of the driven sprocket relative to its initial position (rad); V is the forward speed of the unit (mm/s); ω is the angular velocity of the driven sprocket (rad/s); d is the length of the connecting rod (mm); R is the pitch circle radius of the driven sprocket (mm); h₁ is the length of the hinged support (mm); h₂ is the height of the planter (mm)

To ensure that the absolute horizontal displacement between the planting point Z and the release point S of the Chuanxiong seed stalk approaches zero, according to Equation (1), the following Equation (2) can be obtained:

$${\displaystyle \frac{{\theta }_{1}V}{w}}+(R+h_1)\cos {\theta }_1={\displaystyle \frac{{\theta }_{2}V}{w}}+(R+h_1)\cos {\theta }_2 (0\le {\theta }_1<{\theta }_2<\pi )$$

(2)

where the rotation angle of the driven sprocket at planting point Z is defined as θ₁, and that at release point S is defined as θ₂. Hereafter, θ₁ and θ₂ are referred to as the soil-entry angle and the release angle for the gripping point T, respectively.

Further simplification of Equation (2) yields:

$${\displaystyle \frac{(R+h_1)w}{V}}={\displaystyle \frac{{\theta }_2-{\theta }_1}{\cos {\theta }_1-\cos {\theta }_2}}$$

(3)

The planting speed ratio λ [23] is introduced as the ratio of the linear velocity of the gripping point T to the forward speed V of the machine, as shown in Equation (4).

$$\lambda ={\displaystyle \frac{\left(R+h_1\right)w}{V}}={\displaystyle \frac{{\theta }_2-{\theta }_1}{\cos {\theta }_1-\cos {\theta }_2}}$$

(4)

Using standard trigonometric identities and inequalities, the following relationships hold:

$$\left\{\begin{array}{c}\cos {\theta }_1-\cos {\theta }_2=2\sin {\displaystyle \frac{{\theta }_2+{\theta }_1}{2}}\sin {\displaystyle \frac{{\theta }_2-{\theta }_1}{2}}\\ 0<\sin {\displaystyle \frac{{\theta }_1+{\theta }_2}{2}}\le 1\\ \sin ({\displaystyle \frac{{\theta }_2-{\theta }_1}{2}})<{\displaystyle \frac{{\theta }_2-{\theta }_1}{2}}\end{array} (0\le {\theta }_1<{\theta }_2<\pi )\right.$$

(5)

By substituting the relations in Equation (5) into Equation (4), it can be derived that satisfying the design requirement that the absolute horizontal displacement between the planting point Z and the release point S approaches zero requires λ > 1. When λ ≤ 1, the selection of planting point Z and release point S cannot meet the condition that their absolute horizontal displacement approaches zero, as shown in Figure 3.

Within the value ranges and relative constraints of θ₁ and θ₂ defined in Equation (5), λ values were calculated using Equation (4) to form a dataset for surface fitting. These points, shown as red dots in Figure 4, were used to generate the response surface in OriginPro 2024, which lies entirely above λ = 1, indicating that when the horizontal displacement between the planting point Z and release point S of the Chuanxiong seed stalk approaches zero, λ must exceed 1.

There exists a relationship among the planting frequency f (plants/min), planting spacing D_l (as shown in Figure 2), and the forward speed V of the machine:

$$V={\displaystyle \frac{f}{60}}\times D_l$$

(6)

The planting spacing D_l is:

$$D_l={\displaystyle \frac{\left(2D+2\pi R\right)·V}{NRw}}$$

(7)

where N is the number of planters, and D is the center distance of the chain assembly.

The sum of the driven sprocket radius and the length of the hinged support is defined as the driven sprocket rotation radius R_z, as shown in Equation (8).

$$R_z=R+h_1$$

(8)

The distance between the center of the driven sprocket and the release point is expressed by Equation (9).

$$D_d=R+d+h_1+h_2$$

(9)

When λ > 1, the trajectory of the gripping point T intersects itself. It is a curtate cycloid. For any point located below the longest horizontal chord EE′, there exists a vertically aligned counterpart above it. This allows the planter to adjust the posture of the Chuanxiong seed stalk during planting, maintaining its uprightness.

The planting process of the Chuanxiong seed stalk is shown in Figure 5. When the gripping point is above the longest chord EE′ of the working trajectory, it is the first stage, as shown in Figure 5a. The gripping point T is at the planting point Z, which marks the moment the Chuanxiong seed stalk first contacts the soil. As the machine moves forward and the planting system operates, the gripping point T moves from point Z to point E′. During this period, point T has a horizontal velocity component V_x to the right, in the same direction as the machine’s forward speed, and a vertical velocity component V_y downward toward the soil. The lower part of the Chuanxiong seed stalk is compressed and penetrates into the soil, causing the surrounding soil to sink. The rightward horizontal velocity causes the seed stalk to tilt forward. The cumulative horizontal forward-tilting displacement of the Chuanxiong seed stalk from point Z to point E′, which characterizes the horizontal soil disturbance induced during the forward-tilting stage, is defined as x_t. The Chuanxiong seed stalks’ movement compresses the soil forwards and downwards, while the soil behind falls back and flows. The gripping point T continues moving to point E′. At position in Figure 5b, the horizontal velocity component V_x of the gripping point T becomes zero. Then, the gripping point T moves from point E′ to the release point S. During this period, the gripping point T has a backward horizontal velocity V_x, opposite to the machine’s forward direction, and a downward vertical velocity V_y. During this stage, the planter corrects the forward tilt of the Chuanxiong seed stalk caused by the movement from point Z to point E′. The cumulative horizontal displacement of the Chuanxiong seed stalk from point E′ to point S, which represents the horizontal soil disturbance during the posture-correction stage, is defined as x_c. At position in Figure 5c, the posture of the Chuanxiong seed stalk is shown. The Chuanxiong seed stalk’s movement compresses the soil backwards and downwards, while the soil in front falls back and flows. Finally, the gripping point T reaches the lowest point of its trajectory—the release point S., as shown in Figure 5d. At this moment, its vertical velocity component is zero. The rhizome node presses the soil firmly within the hole, forming a planting cavity. The planter then opens to release the seed stalk, completing the insertion and planting action. The entire planting process of the Chuanxiong seed stalk can be divided into the stages of soil entry, forward tilt, posture correction, and release.

When the gripping point T moves to position E′ in Figure 5b, its horizontal velocity becomes zero. Combining this condition with Equation (1) yields Equation (10):

$${\displaystyle \frac{dx}{d{\theta }_{E^{\prime }}}}={\displaystyle \frac{V}{w}}-(R+h_1)\sin {\theta }_{E\prime }=0$$

(10)

where θ_E′ is the rotation angle of the driven sprocket when the gripping point T reaches point E′.

Furthermore, the rotational angle of the driven sprocket at position E′ can be obtained, as shown in Equation (11):

$${\theta }_{E^{\prime }}=\arcsin \left[{\displaystyle \frac{V}{w(R+h_1)}}\right]$$

(11)

By combining Equations (1) and (11), the horizontal coordinate of position E′ can be obtained, as given in Equation (12):

$$x_{E^{\prime }}={\displaystyle \frac{{\theta }_{E^{\prime }}V}{w}}+(R+h_1)\cos {\theta }_{E^{\prime }}$$

(12)

where x_E′ is the horizontal coordinate of the gripping point T at position E′.

When the gripping point T moves to position S in Figure 5b, the Chuanxiong seed stalk is released. At this moment, the rotational angle of the driven sprocket is θ₂. Combining this with Equation (1), the coordinates of the seed stalk release point S can be obtained. According to the above description of the posture-correction displacement of the seed stalk, Equation (13) is derived as follows:

$$x_c=x_{E\prime }-x_S$$

(13)

where x_S is the horizontal coordinate of the gripping point T at the release point S, and x_C is the horizontal correction of the Chuanxiong seed stalk during the posture-correction stage.

At this moment, the gripping point is close to the soil surface, and the rhizome node of the Chuanxiong seed stalk is in full contact with the soil. According to the seed-stalk geometry shown in Figure 2, the planting depth at this stage is 30 mm. Therefore, the relationship between the vertical coordinate of the seed-stalk release point y_S and that of the soil-entry point y_Z is given by Equation (14):

$$y_Z-y_S=30$$

(14)

where y_Z is the vertical coordinate of the Chuanxiong seed stalk at the soil-entry point Z, and y_S is the vertical coordinate at the release point S.

By combining y_Z with Equation (1), the rotational angle of the driven sprocket at soil entry, θ₁, can be obtained. The horizontal coordinate of the gripping point at soil entry, x_Z, can then be determined. Based on the above analysis, the forward-tilt amount of the Chuanxiong seed stalk at soil entry can be expressed by Equation (15).

$$x_t=x_{E^{\prime }}-x_Z$$

(15)

where x_Z is the horizontal coordinate of the gripping point at the soil-entry point Z, and x_t is the horizontal forward-tilt value of the Chuanxiong seed stalk during the forward-tilt stage.

The relative position between the Chuanxiong seed stalk and the soil surface shown in Figure 5 indicates that the planting depth is determined by the cutting shape of the Chuanxiong seed stalk and the installation position between the planting mechanism and the ground. The shape of the planting trajectory affects the planting verticality of seed stalks. The key factor influencing the trajectory curve is the planting speed ratio λ. As shown in Equations (4) and (8), under a fixed horizontal motion speed of the planting mechanism, the main factors affecting the trajectory curve shape are the angular velocity ω of the driven sprocket and the rotation radius R_z of the sprocket. By designing the angular velocity ω and the rotation radius R_z, the trajectory of the planting mechanism can be adjusted to improve the verticality of Chuanxiong seed stalk planting. In addition, the timing of Chuanxiong seed stalk release also affects the planting verticality. Since the motion of the planter is driven by the driving sprocket of the planting mechanism, the release timing can be expressed as the rotation angle θ₂ of the driven sprocket corresponding to the moment of Chuanxiong seed stalk release. The following sections will optimize the angular velocity ω of the driven sprocket, the rotation radius R_z, and the release angle θ₂, ensuring compliance with the traditional agronomic requirements for planting spacing of Chuanxiong seed stalks, while further improving the uprightness of the planted seedlings.

2.3. Parameter Analysis and Simulation of the Planting Mechanism

2.3.1. Fundamental Parameter Analysis of the Planting Mechanism

Based on market research, the conventional tooth number of finished 08A sprockets ranges from 12 to 40. To enhance the stability of chain transmission, a sprocket with z = 40 is preferably selected as the driving sprocket [24,25]. Given a chain pitch p = 12.7 mm, the rotation radius R is calculated as 80.93 mm according to Equation (16).

$$R={\displaystyle \frac{p}{2\sin (\frac{180°}{z})}}$$

(16)

In Figure 3, the setting of the eccentric distance d refers to the conventional range (typically 50~80 mm) for eccentric rice wheels [26]. Accordingly, the eccentric distance of the chain group is set to d = 50.8 mm (an integer multiple of the chain pitch p = 12.7 mm) [27]. The center distance D of the chain group is related to the structural parameters of the chain, as shown in Equation (17).

$$D=p\left[{\displaystyle \frac{ L_p-z}{2}}\right]$$

(17)

The number of chain links L_p should be an integer multiple of the number of planter N. Since the movement of the planter requires a segment with no horizontal displacement for stable seed stalk pickup, the number of planter segments is set to N = 6, and the number of chain links is set to L_p = 78. According to Equation (17), the center distance of the chain group is D = 241.3 mm.

Based on the selection of certain components of the planting system, the distance between the planting system and the soil surface is set to D_d = 230 mm. Based on Equation (9) and the chain group eccentricity d = 50.8 mm, the relationship between the driven sprocket rotation radius R_z and the height of the planter h₂ is given in Equation (18).

$$R_z+h_2=179.2$$

(18)

2.3.2. DEM-MBD Coupled Simulation of Planting Mechanism

The DEM–MBD bidirectional coupling numerical simulation allows direct observation of the complex motion of the Chuanxiong seed stalk and its disturbance to soil particles.

In Figure 6, a soil particle bed with dimensions of 200 mm × 120 mm × 80 mm was established. The particle in the bed model is generated, as shown in Figure 6a. The physical parameters of the seed stalks and the contact parameters between Chuanxiong seed stalks and soil were set based on relevant literature [28,29,30]. The specific simulation parameters are listed in

Table 1. Simulation parameters of the Chuanxiong seed stalk discrete element model.

Type	Parameter	Value
Chuanxiong seed stalk	Poisson’s ratio	0.41
	Shear modulus (MPa)	390.6
	Density (g·cm−3)	0.574
Soil	Poisson’s ratio	0.38
	Shear modulus (MPa)	1.86 × 106
	Density (kg·m−3)	1366
Chuanxiong seed stalk-Soil	Coefficient of restitution	0.5
	Static friction coefficient	0.83
	Rolling friction coefficient	0.7

.

A discrete element method (DEM) simulation was established to verify the reasonableness of the parameter settings for the Chuanxiong seed stalk and soil. The simulation process is shown in Figure 6a. The seed stalk descent speed was set to 10 mm/s. After the simulation, the force diagram on the Chuanxiong seed stalk was exported, as shown in Figure 6b. When the node disc of the Chuanxiong seed stalk was half exposed, the bottom of the seed cane was about 30~35 mm below the top layer of the DEM soil, meeting the agronomic requirements for Chuanxiong planting, and the maximum insertion resistance was 10~13 N.

To ensure the accuracy of the simulation results, a soil resistance test was designed to measure the soil resistance during the planting of Chuanxiong seed stalks. The test was conducted in late August, the optimal planting period for Chuanxiong seed stalk. Soil samples were collected from a Chuanxiong rhizome planting field located in Aoping Town, Pengzhou City, Sichuan Province (approximately 31.0939° N, 103.9869° E) after rotary tillage and ridge formation, with a sampling depth of 0~45 mm. The soil at the test site was classified as sandy loam, with an average water content of 11.04% and a bulk density of 1.366 kg·m⁻³. Before testing, the soil surface in the container was leveled to ensure uniform force distribution. The test procedure was conducted on a universal material testing machine, as shown in Figure 6c. A wedge-shaped fixture held the Chuanxiong seed stalk on the node disc and adjusted it to keep the seed stalk perpendicular to the soil surface. The fixture descended at a speed of 10 mm/s until the node disc was half exposed, at which point the downward movement stopped. Load–displacement curves were recorded, and the test results are shown in Figure 6d. In Figure 6d, curves 1, 2, and 3 represent the results of three repeated insertion tests under the same experimental conditions. These soil samples and test conditions reflect the field soil conditions after rotary tillage, ensuring that the results are representative of actual field planting.

In Figure 6d, the test results show that under good tillage conditions, Chuanxiong seed stalks can be directly inserted into the soil until the node disc is half exposed. At this point, the bottom of the seed stalk is about 30~35 mm below the soil surface, meeting the agronomic requirements for Chuanxiong planting, and the maximum insertion resistance is 10~13 N.

To validate the realism of the soil model used in the DEM simulation, the insertion resistances of Chuanxiong seed stalks showed similar trends. Six characteristic penetration depths (5, 10, 15, 20, 25, and 30 mm) were selected from the simulated force–depth curve in Figure 6b, and the corresponding forces were compared with the experimental measurements in Figure 6d, using curve 3 as the reference. The relative error at each depth was calculated using Equation (13).

$${\delta }_i={\displaystyle \frac{|F_{sim,i}-F_{exp,i}|}{F_{exp,i}}}\times 100\%$$

(19)

where F_sim,i is the simulated insertion force and F_exp,i is the experimentally measured insertion force at the same penetration depth.

The relative errors of the DEM simulation compared with the experimental results are listed in

Table 2. Relative errors of simulated insertion forces compared with experimental measurements.

Penetration Depth/mm	Fsim,i/N	Fexp,i/N	Relative Error/%
5	0.75	0.66	13.64
10	1.44	1.55	7.10
15	2.30	2.60	11.54
20	3.85	4.18	7.90
25	7.75	7.28	6.46
30	11.58	10.21	13.42
Average	/	/	10.01

.

The results are summarized in Table 2. The relative errors ranged from 6.46% to 13.64%, with an average of 10.01%, indicating that the DEM soil model can reliably represent the real soil conditions after rotary tillage and accurately reproduce the insertion behavior of Chuanxiong seed stalks (Figure 7).

To validate the robustness of the DEM simulation results presented in Table 2, a sensitivity analysis was conducted on three critical input parameters. The static friction coefficient (μ_s) was selected because it governs the interfacial shear strength between the seed stalk and soil particles, directly influencing the insertion resistance [31]. The soil shear modulus (G_soil) determines the mechanical response of the granular bed under compression [32]. The stalk shear modulus (G_stalk) controls the elastic deformation of the planting object during penetration.

The simulated insertion forces at the target planting depth of 30 mm (corresponding to 3 s in the simulation) were analyzed for parameter sensitivity. Notably, the sensitivity of insertion resistance to these parameters was observed to increase with insertion depth, with the most pronounced effects occurring near the target depth (2–3 s). The reference insertion force using the original parameters (μ_s, G_soil, G_stalk) was 11.24 N. Increasing μ_s by 10% raised the force to 12.259 N, while decreasing μ_s by 10% reduced it to 10.325 N, corresponding to an average sensitivity of 8.6%. Similarly, G_soil showed a relatively high influence, with forces of 12.339 N and 10.045 N for +10% and −10% variations, respectively (average sensitivity 10.2%). The stalk shear modulus G_stalk had a moderate effect, with forces of 12.24 N and 10.525 N for ±10% changes, yielding an average sensitivity of 7.7%. These results indicate that the simulation is reasonably sensitive to soil parameters, particularly interfacial friction and soil modulus, while the model is moderately robust to natural variations in stalk mechanical properties.

The DEM-MBD bidirectional coupling has achieved through the dedicated RecurDyn–EDEM co-simulation interface. To account for randomness in the simulation tests, the soil particle bed was regenerated before each of the DEM-MBD co-simulation trials. A simplified 3D model of the planting mechanism was built using ‘SolidWorks 2016’ and imported into ‘RecurDyn 2024’. Based on the previous structural design, constraints, contacts, and transmission relationships between components were defined. The simulation model of Chuanxiong seed stalks was imported, and contact between the seed stalks and the planter’s gripper was established. The dynamic and static friction coefficients between the seed stalks and the gripper were set to 0.517 and 0.546, respectively [33]. In addition, the operating speed of the planter V and the angular velocity of the passive sprocket ω were specified, with their directions shown in Figure 8a.

The simulation began when the seed stalk gripping point of the planter reached position A in Figure 3, during which the Chuanxiong seed stalk moved with the planter and was inserted into the soil. At the moment of release, the passive sprocket had rotated to an angle of θ₂, which is illustrated in Figure 8b.

As shown in Figure 9, Marker1 and Marker2 were arranged at the top and bottom of the seed stalk to determine its axial direction relative to the soil surface. The coordinates of the two markers were obtained from the simulation results, and the planting uprightness was calculated using Equation (20). A higher uprightness value corresponds to better planting quality [34].

$$\beta =\arctan \left({\displaystyle \frac{\left|y_2-y_1\right|}{\left|x_2-x_1\right|}}\right)$$

(20)

3. Results and Discussions

3.1. Analysis of Simulation Results

3.1.1. Single Factor Analysis of Simulation

According to the relevant technical specification, the recommended planting spacing for Chuanxiong seed stalk planters is 180~200 mm [35]. In accordance with the planting efficiency requirements, the horizontal speed of the planting mechanism was set to 60 mm/s. The rotation angular velocity range of the driven sprocket ω is obtained with reference to the spacing calculation Equation (7) and the determined parameters (sprocket radius R, center distance of the chain assembly D, number of planting devices N), and is selected as 0.62~0.70 rad/s. In Figure 1, the connection between the chain joint and the hinged support is riveted. To reduce the shear force on the rivet during operation and considering the planter width, the height of the hinged support h₁ was selected as 19~23 mm. Based on Equations (8) and (16), the rotational radius of the driven sprocket R_z was determined to range from 99.93 to 103.93 mm. The release timing of the Chuanxiong seed stalk also affects planting uprightness. In this study, a curtate cycloid was adopted as the planting trajectory. Considering the symmetry of the planting trajectory, the release angle, θ₂, was set with 90° as the reference value, and a preliminary range of 84°~96° was selected. The factor level values are shown in

Table 3. Single-factor test parameters.

Level	Driven Sprocket Angular Velocity	Driven Sprocket Rotational Radius	Release Angle
1	0.62	99.93	84
2	0.64	100.93	87
3	0.66	101.93	90
4	0.68	102.93	93
5	0.70	103.93	96
Baseline	0.66	101.93	90

.

Single-factor simulation results are as follows:

(1)

The effect of the angular velocity of the driven sprocket w on the planting uprightness of Chuanxiong seed stalks is shown in Figure 10a. As the rotation speed increases, the planting uprightness first rises to a peak and then decreases. To maintain good uprightness, the angular velocity w should be set between 0.64 rad/s and 0.68 rad/s.

(2)

The effect of the rotational radius of the driven sprocket R_z on the planting uprightness of Chuanxiong seed stalks is shown in Figure 10b. As R_z increases, the uprightness initially rises rapidly and then gradually declines. To ensure good planting uprightness, the rotation radius R_z should be set in the range of 99.93 mm to 101.93 mm.

(3)

The effect of the release angle θ₂ on the planting uprightness of Chuanxiong seed stalks is shown in Figure 10c. As θ₂ increases, the planting uprightness gradually increases, reaches a peak, and then rapidly decreases. To maintain good planting uprightness, the release angle θ₂ at the release point should be set between 87° and 93°.

3.1.2. Regression Orthogonal Experimental Analysis

To obtain the optimal values of the three factors, a Box–Behnken experimental design was conducted using ‘Design-Expert 12.0’ [36] software. Based on the single-factor simulation results, the angular velocity of the driven sprocket w, the rotational radius of the driven sprocket R_z, and the release angle θ₂ were identified as key factors affecting the planting uprightness of Chuanxiong seed stalks. The factor levels are shown in

Table 4. Factor level codes of the test.

Level	Driven Sprocket Angular Velocity A (rad/s)	Driven Sprocket Rotational Radius B (mm)	Release Angle C (°)
−1	0.64	99.93	87
0	0.66	100.93	90
1	0.68	101.93	93

.

The planting uprightness Y of Chuanxiong seed stalks was used as the evaluation indicator for the simulation tests. A total of 17 experimental groups were set, including 5 zero-point tests (m0 = 5). After excluding data with significant differences, the average value was taken as the test result. The experimental plan and results are shown in

Table 5. Experimental scheme and results.

Test Groups	Test Factors			Test Results
	A (rad/s)	B (mm)	C (°)	Y (°)
1	0	0	0	85.34
2	1	−1	0	82.35
3	0	1	1	75.2
4	−1	0	−1	74.36
5	0	0	0	85.28
6	0	1	−1	78.54
7	1	1	0	74.14
8	−1	−1	0	78.84
9	0	0	0	85.43
10	0	−1	−1	76.41
11	0	0	0	83.85
12	0	−1	1	80.88
13	0	0	0	84.69
14	1	0	1	73.44
15	1	0	−1	77.89
16	−1	1	0	81.82
17	−1	0	1	83.6

.

In Table 5, the highest planting uprightness of Experiment Group 1 is 85.34°, while the lowest planting uprightness of Experiment Group 14 is 73.44°. There is a significant difference between the simulation results of Group 1 and Group 14. The regression analysis results for planting uprightness Y are shown in

Table 6. Variance analysis of simulation results.

Source	Planting Uprightness
	Sum of Square	df	Mean Square	F	p
Model	293.51	9	32.61	50.20	<0.0001
A	14.58	1	14.58	22.44	0.0021 **
B	9.64	1	9.64	14.83	0.0063 **
C	4.38	1	4.38	6.74	0.0356 *
AB	31.30	1	31.30	48.19	0.0002 **
AC	46.85	1	46.85	72.12	<0.0001 **
BC	15.25	1	15.25	23.47	0.0019 **
A2	38.73	1	38.73	59.61	0.0001 **
B2	28.41	1	28.41	43.74	0.0003 **
C2	87.66	1	87.66	134.93	<0.0001 **
Residue	4.55	7	0.6497	/	/
Lack of fit	2.78	3	0.9279	2.10	0.2424
Error	1.76	4	0.4410	/	/
Sum	298.06	16	/	/	/

Note: ** means highly significant (p ≤ 0.01): * means significant (0.01 < p < 0.05), / indicates that no value was obtained, same as below.

.

The regression model for the planting uprightness of Chuanxiong seed stalks is highly significant (p < 0.0001), with a coefficient of determination R² = 0.98, an adjusted R² = 0.96, and a coefficient of variation CV = 1.01%. The non-significant lack-of-fit test (p = 0.2424) indicates that the second-order polynomial model adequately fits the simulation data. Among the factors, the quadratic term of the release angle (C²) has the most pronounced effect, followed by the interaction term AC and the quadratic terms of A² and B². The significance of interaction terms AB, AC, and BC demonstrates that the combined effects of the driven sprocket angular velocity, rotation radius, and release angle cannot be ignored. Overall, the model provides a reliable basis for optimizing the key parameters to maximize planting uprightness.

Based on Table 6, regression fitting analysis was performed using Design Expert 12 software, and a second-order polynomial response surface regression model was established for the planting uprightness Y of Chuanxiong seed stalks, with the angular velocity of the driven sprocket A, the rotational radius of the driven sprocket B, and the release angle C, as shown in Equation (21).

$$Y=84.92-1.35A-1.1B+0.74C-2.8AB-3.42AC-1.95BC-3.03A^2-2.6B^2-4.56C^2$$

(21)

Equation (14) shows the significance ranking of the factors affecting the planting uprightness of Chuanxiong seed stalks as follows: the angular velocity of the driven sprocket > the rotational radius of the driven sprocket > the release angle.

Based on the regression equation analysis, response surface plots were generated using ‘Design-Expert’ 12.0 software to study the interaction effects of the factors on the planting uprightness of Chuanxiong seed stalks, as shown in Figure 11. The color gradient from red, yellow, and green to blue represents the planting uprightness from high to low.

The response surface curves illustrating the effects of the angular velocity of the driven sprocket A, the rotational radius of the driven sprocket B, and the release angle C on the planting uprightness Y of Chuanxiong seed stalks are shown in Figure 11a–c.

Figure 11a shows the effects of the angular velocity of the driven sprocket A and the rotational radius of the driven sprocket B on the planting uprightness Y of Chuanxiong seed stalks when the release angle C is 90°. It can be observed that, with a decrease in the angular velocity of the driven sprocket A and an increase in the rotational radius of the driven sprocket B, the planting uprightness Y of Chuanxiong seed stalks first increases and then decreases.

Figure 11b shows the effects of the angular velocity of the driven sprocket A and the release angle C on the planting uprightness Y of Chuanxiong seed stalks when the rotational radius of the driven sprocket B is 100.93 mm. It can be observed that, with a decrease in the angular velocity of the driven sprocket A and an increase in the release angle C, the planting uprightness Y of Chuanxiong seed stalks first increases and then decreases.

Figure 11c shows the effects of the rotational radius of the driven sprocket B and the release angle C on the planting uprightness Y of Chuanxiong seed stalks when the angular velocity of the driven sprocket A is 0.66 rad/s. It can be observed that, with a decrease in the rotational radius of the driven sprocket B and an increase in the release angle C, the planting uprightness Y of Chuanxiong seed stalks first increases and then decreases.

3.1.3. Optimization of Parameters and Simulation-Based Planting Verification

The optimization goal is to maximize the planting uprightness of Chuanxiong seed stalks. The parameters of the angular velocity of the driven sprocket, the rotational radius of the driven sprocket, and the release angle are optimized using ‘Design-Expert’ 12.0 software. The optimization objective function and constraints are shown in Equation (22).

$$\left\{\begin{array}{l}\max Y(A,B,C)\\ s.t. 0.64 \mathrm{rad}/\mathrm{s}\le A\le 0.68 \mathrm{rad}/\mathrm{s}\\ 99.93 \mathrm{mm}\le B\le 101.93 \mathrm{mm}\\ {87}^{°}\le C\le {93}^{°}\end{array}\right.$$

(22)

The optimal parameter combination for the planting mechanism is obtained as follows: the angular velocity of the driven sprocket is 0.654 rad/s, the rotational radius of the driven sprocket is 100.787 mm, and the release angle is 90.647°. For practical engineering implementation, these values were rounded to 0.65 rad/s, 100.79 mm, and 90.6°, respectively. At this point, the planting uprightness of Chuanxiong seed stalks is 85.264°.

Following parameter optimization, five simulation runs were performed to assess the planting performance of Chuanxiong seed stalks. An upright angle of 70° or higher was used as the qualification criterion. The simulated upright angles were 87.5°, 84.2°, 85.7°, 84.9°, and 86.1°, resulting in a qualification rate of 100%. These results show that the optimized parameters consistently produce acceptable planting postures in simulation, providing confidence in the design before field validation.

Based on the optimized parameters and previously calculated values, the parameters of the cuttage planting mechanism for Chuanxiong seed stalks are summarized in

Table 7. Structural parameters of the planting mechanism.

Parameters	Values
Planting speed ratio λ	1.099
Pitch circle radius of the driven Sprocket R/mm	80.93
Tooth number	40
Chain pitch p/mm	12.7
Number of chain links Lp	78
Number of planters N	6
Eccentricity of the chain assembly d/mm	50.8
Center distance of the chain assembly D/mm	241.3
Planting spacing Dl/mm	187.31
Radial distance between crank hinge point and the chain h1/mm	19.9
Height of the planter h2/mm	78.37

, according to Equations (7), (8), and (18).

By combining the optimized parameters with Equation (1), the ideal motion trajectory of the Chuanxiong seed-stalk gripping point of the planter can be obtained, as shown in Figure 12.

After optimization, the release angle θ₂ is 90.65°. By combining Equation (1) with the optimized parameters in Table 7, the coordinates of the seed-stalk release point S are obtained as (144, −229.99). Using Equations (11)–(13), the posture-correction amount x_c is calculated to be 2.69 mm. Furthermore, based on the coordinates of point S together with Equations (1), (14), and (15), the forward-tilt amount x_t is 5.18 mm, and the soil-entry angle θ₁ is 44.62°.

Using the optimized parameters, a DEM-MBD coupled numerical simulation was conducted. In the ‘EDEM 2023’ software, the Clipping tool was used to slice the soil particle bed to show the posture changes in the Chuanxiong seed stalk. The posture changes in the Chuanxiong seed stalk were observed from a side view of its movement direction, as shown in Figure 13. The entire planting process of Chuanxiong seed stalks can be divided into four stages: soil entry, forward tilting, posture correction, and release. In Figure 13a,b, it was observed that the Chuanxiong seed stalk was in the soil entry and forward tilting stages from 0.18 s to 1.1 s, during which it was constrained by both the planter and the soil. During this time, its posture began to tilt forward, and the tilt angle increased with the depth of insertion. In Figure 13b,c, the Chuanxiong seed stalk entered the posture correction stage from 1.1 s to 1.5 s, during which its posture started to straighten vertically. The tilt angle gradually decreased as the seed stalk went deeper into the soil, creating the ‘correction’ effect of the planter. At 1.5 s, when the planting operation reached the designated time node at 1.5 s, the planter released the seed, which then stabilized in the soil with a post-planting upright angle of 87.54°, as shown in Figure 13c.

In Figure 13, three specific time points (0.18 s, 1.1 s, and 1.5 s) were selected for analysis. At 0.18 s, the Chuanxiong seed stalk begins to insert into the soil, maintaining a certain velocity as it does so. When Chuanxiong seed stalks insert into the soil, the velocity variation in soil particles induced by the seed stalks’ compression and contact is most significant, and the stem segment exerts the most obvious disturbance on the soil particles, as illustrated in Figure 13a. In Figure 13b, 1.1 s corresponds to the moment when the Chuanxiong seed stalk reaches its maximum tilt. At 0.18 s, the Chuanxiong seed stalk first comes into contact with the soil, initiating the soil–stalk interaction. During the subsequent forward tilting process, the soil in front of the Chuanxiong seed stalk is initially compressed and gradually tends toward a stable state as the motion continues. Meanwhile, the soil behind the Chuanxiong seed stalk shows a movement trend toward the hole formed by the seed’s forward tilt. As the Lingzhong sinks, the node disc compresses the surface soil, causing the soil particles beneath it to move downward under pressure. At 1.5 s, when the planter releases the seed, the final planting posture is established, and the node disc of the Chuanxiong seed stalk contacts the soil. After the planter releases the seed, both the seed stalk and soil particles stabilize, completing the planting of the Chuanxiong seed stalk, as shown in Figure 13c.

3.2. Field Verification Test

3.2.1. Field Test Conditions

To test the performance of the cuttage planting mechanism in the field, the mechanism was installed on a Ligusticum chuanxiong planting machine. A machine was equipped with five sets of planting mechanisms. Before planting, the field was prepared using a rotary tiller to ensure the soil was finely fragmented and the soil surface was relatively leveled. The operation was performed in slow-speed mode on the tractor, with the driving speed controlled at 60 mm/s.

The field operation process of the cuttage planting machine is shown in Figure 14a. The planter grips the Chuanxiong seed stalk from the seed preparation platform and transports the seed along the chain. Then, the planter presses the seed into the soil, entering the planting stage. Finally, the planter releases the seed and slowly moves away from the soil along the chain, entering the return stage.

Instruments and devices used: the cuttage planting machine, steel ruler, protractor, tape, etc.

3.2.2. Test Methods and Performance Indicators

According to the five-point method specified in the standard [37], a test area was selected on the planted ridge, with a length of 1 m and a width equal to the ridge width. According to the technical specifications for the quality of the Chuanxiong seed stalk planter, the plant spacing qualification rate, planting depth qualification rate, and planting uprightness within each test area were evaluated [38].

(1)

Qualified Rate of Plant Spacing

After planting, the plant spacing values within each test area were recorded. A spacing value is considered qualified if it falls within the target plant spacing range of 180–200 mm. The qualified rate of plant spacing for the Ligusticum chuanxiong planting machine was calculated using Equation (23).

$${\alpha }_i={\displaystyle \frac{J_i}{G_i}}\times 100\%$$

(23)

where α is the qualified rate of plant spacing; i denotes the index of the test area; Jᵢ is the number of qualified plant spacing values in the i-th test area; Gᵢ is the total number of measured plant spacing values in the i-th test area.

(2)

Qualified Rate of Planting Depth

After planting, the number of Chuanxiong seed stalks meeting the planting depth requirement was recorded in each test area. The planting system requires that the node disc to be in close contact with the soil or partially exposed, with a qualified planting depth defined as H = 30 ± 3 mm. The qualified rate of planting depth for the Ligusticum chuanxiong planting machine was calculated according to Equation (24).

$${\gamma }_i={\displaystyle \frac{M_i}{N_i}}\times 100\%$$

(24)

In the equation, γ is the qualified rate of planting depth; i denotes the index of the test area; Mᵢ is the number of Chuanxiong seed stalks meeting the planting depth criteria in the i-th test area; Nᵢ is the total number of seed stalks planted in the i-th test area.

(3)

Qualified Rate of Planting Uprightness

After planting, the verticality of Chuanxiong seed stalks was measured in each test area. Seed stalks with a stem-to-ridge surface angle greater than or equal to 70° after planting were considered to meet the verticality requirement. The qualified rate of planting uprightness was calculated using Equation (25):

$${\epsilon }_i={\displaystyle \frac{Q_i}{N_i}}\times 100\%$$

(25)

In the equation, ε is the qualified rate of planting uprightness; i denotes the index of the test area; Qᵢ is the number of the seed stalks with qualified uprightness in the i-th test area; Nᵢ is the total number of the seed stalks planted in the i-th test area.

The mean value of a set of measurements in the test areas was calculated as follows:

$$\overline{X}={\displaystyle \frac{1}{n}}{\displaystyle \sum _{i=1}^n{X}_i}$$

(26)

where $\overline{X}$ is the average value, X_i is the measurement from the i-th test area, and n is the total number of test areas.

To evaluate the variability of the field test results, the mean values of the three qualification rates were calculated using Equation (26). The standard deviation (SD) and coefficient of variation (CV) were calculated using Equations (27) and (28), respectively:

$$SD=\sqrt{{\displaystyle \frac{1}{n-1}}{\displaystyle \sum _{i=1}^n{(X_i-\overline{X})}^2}}$$

(27)

$$CV={\displaystyle \frac{SD}{\overline{X}}}\times 100\%$$

(28)

where X_i is the qualified rate obtained from the i-th test area, and $\overline{X}$ is the corresponding mean value.

The operational quality statistics of the planting mechanism of the cutting-type Ligusticum chuanxiong planter are shown in

Table 8. Statistical Results of Field Measurements for the Planting Mechanism.

Test Area	Ji/Plants	Gi/Plants	Mi/Plants	Qi/Plants	Ni/Plants	α/%	γ/%	ε/%
1	22	24	32	32	34	91.67	94.12	94.12
2	21	25	26	26	27	84	96.30	92.59
3	19	23	30	28	31	82.61	96.77	90.32
4	24	27	28	25	28	88.89	100.00	89.29
5	23	26	26	24	28	88.46	92.86	85.71
Mean	/	/	/	/	/	87.13	96.01	90.41
SD	/	/	/	/	/	3.36	2.63	3.40
CV (%)	/	/	/	/	/	3.86	2.74	3.76

.

As shown in Table 8, the mean qualified rates for plant spacing, planting depth, and planting uprightness are 87.53%, 96.01%, and 90.41%, respectively. The corresponding coefficients of variation are 4.37%, 2.95%, and 3.73%, indicating consistent and stable field test results [39]. These results confirm that the cutting-type planting mechanism performs reliably under actual field conditions and meets the agronomic requirements for Ligusticum chuanxiong planting. The slightly lower uprightness in field tests compared with simulation results is mainly attributed to natural soil heterogeneity, seed stalk variability, and operational disturbances that are not captured in the numerical model.

4. Conclusions

To address the challenges posed by the lack of specialized machinery meeting the traditional agronomic requirements of Chuanxiong, a novel cuttage planting mechanism was developed to directly grip and insert the seed stalks, integrating soil penetration, insertion, and posture regulation into a unified soil–plant–machine interaction. Unlike conventional planters that rely on hole formation, this mechanism achieves direct insertion while simultaneously regulating stalk posture, thereby improving planting quality while ensuring uprightness. Planting uprightness was used as the evaluation index, with the driven sprocket’s angular velocity, rotation radius, and release angle selected as the key test factors. Considering the constraints of planting spacing, planting depth, and soil–stalk interaction, DEM–MBD simulations, single-factor tests, and orthogonal experiments were conducted to optimize the critical structural and motion parameters. Soil disturbance and stalk posture evolution were jointly evaluated to verify feasibility and reliability, and field tests were conducted under sandy loam soil conditions to assess overall performance. The main conclusions are as follows:

(1)

A cuttage planting mechanism for Chuanxiong seed stalks was presented, and its overall structure and working principle were described and analyzed. The planting process was divided into four stages: soil entry, forward tilt, posture correction, and release. Based on this staged process, the posture variation in the Chuanxiong seed stalk during planting was analyzed, and two quantitative posture indicators were defined: the horizontal forward-tilt value x_t during the forward-tilt stage and the horizontal correction value x_c in the subsequent correction stage.

(2)

The mathematical models of the planting trajectory were established. Based on the relative motion and positional relationships between the planting device and the ground, the spacing and planting depth calculation equations were derived to ensure that the planting trajectory satisfies the requirements for spacing and planting depth. Through kinematic analysis, the planting speed ratio λ was defined. The results indicate that when λ > 1, the planting trajectory corresponds to a curtate cycloid, which satisfies the uprightness requirement for Chuanxiong seed stalk planting. After optimization, the value of λ was 1.099.

(3)

Under the constraints of planting spacing and depth, the DEM–MBD coupled simulation experiment was designed and conducted. A three-factor, three-level quadratic regression orthogonal design was adopted, with planting uprightness as the evaluation index. The results show that the effects on planting uprightness decrease in the following order: angular velocity of the driven sprocket > rotational radius of the driven sprocket > release angle. Through multi-objective optimization, the optimal parameters were determined as an angular velocity of 0.654 rad/s, rotation radius of 100.787 mm, and release angle of 90.647°. Under these conditions, the average planting verticality reached 85.264°. Based on the optimized parameters, the horizontal forward-tilt value during the forward-tilt stage was x_t = 5.18 mm, and the horizontal correction in the subsequent correction stage was x_c = 2.69 mm, quantitatively confirming the corrective effect of the curtate cycloid trajectory on the posture of the Chuanxiong seed stalk.

(4)

Field tests were conducted on the prototype machine, using average plant spacing qualification rate (agronomic standard: 180–200 mm), average planting depth qualification rate (agronomic standard: 30 ± 3 mm), and average planting uprightness qualification rate (agronomic standard: ≥70°). The results were 87.13%, 96.01%, and 90.41%, respectively, with corresponding coefficients of variation of 4.37%, 2.95%, and 3.73%. These results indicate that the proposed Chuanxiong seed stalk planting mechanism can achieve stable and reliable performance under field conditions, meeting the above-specified agronomic requirements.

Compared with conventional soil-opening-based planting methods, the proposed mechanism can more precisely regulate the posture of Chuanxiong seed stalks, thereby improving planting quality. However, it requires a higher level of field preparation, including thorough rotary tillage and leveling, prior to operation, and is currently best suited for sandy loam soil conditions. Although this study introduced the quantitative posture indicators x_t and x_c to characterize the planting trajectory, further optimization of the trajectory in combination with seed placement and hole formation was not considered. This could serve as a potential direction for future research.