Design and Experiment of Sweet Potato Up-Film Transplanting Device with a Boat-Bottom Posture

Abstract

Aimed at solving the problem of the incidence of large film-breaking holes in the current sweet potato boat-bottom-shaped transplant, a boat-bottom-shaped up-film transplanting device was designed. Starting from the agronomic requirements of sweet potato up-film transplanting with a boat-bottom posture, an arc-shaped gripping mechanism was designed. In order to avoid further tearing and breaking the film hole during the movement of the clamping mechanism under the membrane, a transposition mechanism and a positioning cam were designed to jointly control the movement of the clamping mechanism. In order to ensure the stability of the transplanting plant spacing during the operation of the machine, a rotary encoder was used to collect the forward speed of the machine and adjust the speed of the power shaft in real time. Field experiments were carried out in order to verify the reliability and stability of the operation of the above-mentioned design mechanism. In the field test, the advance speed was used as the test factor, and the test indexes included three indexes of the seedlings after transplanting and three indexes of the film holes. The test results showed that the qualified rate of node depth in the middle of the seedling (QRNDMS) is between 95.67% and 86.79%, the qualified rate of root depth at the base of the seedlings (QRRDS) is between 94.00% and 90.11%, and the qualified rate of seedling length into the soil (QRSLS) is between 97.89% and 91.67%. The film hole spacing is between 240.33 mm and 245.32 mm, the film hole length is between 37.01 mm and 42.10 mm, and the film hole length variation rate is between 1.05% and 7.48%. This study can serve as a reference for up-film transplantation, particularly for boat-bottom-shaped up-film transplantation devices.

1. Introduction

Sweet potato is an important food in China, and sweet potato cultivation is an important part of the sweet potato industry. Farmers plant sweet potatoes using methods that employ straight [1], oblique [2], flat [3], boat-bottom-shaped [4], and pressed rattan devices [5]. According to Li [6], Wu [7], and other researchers, the planting method that uses the boat-bottom-shaped device has the highest yield of all five transplanting methods that have been tested in the field. Ma [8], Luo [9], and others found that the mulching one increased the yields by over 16% when it was compared to not performing the mulching one, with the opaque black mulching method outperforming the transparent mulching method. In order to increase the yield of the sweet potatoes, the best method is to spread black plastic film before the boat-bottom transplanting has been performed. The process of using the boat-bottom-shaped transplanting device is performed after the mulching has been performed, and this requires precision in the planting mechanism’s trajectory, and the current equipment can only make straight and oblique insertions [10]. As a consequence, it is very important for Chinese food security operators to find an approach to transplanting sweet potatoes with smaller holes in the film.

Some researchers employ the ground wheel drive one [11], the self-propelled type [12], and other approaches to combat the forward speed shift impacting the transplanting device’s trajectory. The rotation speed of the ground wheel is detected by the rotary encoder to control the transplanting speed of the planting mechanism so as to reduce the variation coefficient of plant spacing [13]. Hu et al. [14] (p. 10) planted sweet potato seedlings obliquely by combining the machine’s forward speed and transplanting speed to form a trochoid movement trajectory. Zhu [15] constructed a four-link transplanting mechanism and used Matlab to modify its settings, thus enabling more the precise oblique transplantation of the sweet potato seedlings. Pan et al. [16] and Zhang [17] built a mathematical model of the transplanting device’s movement, optimized the design parameters, and verified the machine’s performance through conducting field tests. The aforementioned research focuses on non-membrane transplantation, the selection of the transplanting mechanism’s structural form, and the optimization of its structural characteristics or operating parameters. The end of the transplanting mechanism’s movement trajectory is very consistent with the seedling’s posture in the soil after transplanting it to meet the agronomic requirements. However, these research methods cannot solve the problem of performing transplanting them after the film mulching has taken place.

After the structural parameters of the transplanting mechanism have been determined, if the coefficient of the variation of the plant spacing is too large, then this will cause a large difference between the actual size of the membrane pores and the theoretical size of the membrane pores. Therefore, keeping the plant spacing stable is a prerequisite for discussing the size of the membrane pores. Engineers alter the transplanting mechanism’s structural properties to reduce the membrane-breaking hole size. Du and et al. [18] established a soil stratification model to account for the occurrence of planting resistance. This model was merged with the planting mechanism’s core motion principle, and its motion equations were inferred. The computer simulations show that performance of the transplanting process onto a vertical film is feasible. Liu et al. [19] examined the planting mechanism’s motion requirements and trajectory formation concept to create a kinematic model. A human–computer interaction analysis program optimizes the mechanism’s parameters for greater verticality before and after the transplanting process. High-speed video tests of the bench show that the actual motion trajectory is extremely consistent with the theoretical one that is needed for the trajectory, and thus, vertical planting on the membrane can be performed well. Xu [20] created a vertical planting mechanism to increase Salvia miltiorrhiza’s transplanting rate. Using the working condition constraints, free motion restrictions, and a kinematics model, a visualization assistance interface was created. The influence of each mechanism parameter on the movement trajectory and end-point attitude was explored, and a better set of parameters was established using numerical cyclic comparisons. In the field, the membrane-breaking hole is smaller, and the seedling rate is higher. Zhou [21] designed a differential planetary gear train to drive a four-bar planter to transplant the pot seedlings on a membrane. The development of an optimization design software improved the parameter group and enabled the vertical film transplanting of pepper seedlings. The objective of the above research is to make the transplanting mechanism move up and down in a straight line to achieve a high seedling standing rate and small membrane-breaking holes, and the above-mentioned machines and tools only allow for vertical transplanting to take place, which is insufficient for the boat-bottom-shaped up-film sweet potato transplanting device.

In this work, a device for the performance of transplanting after that of mulching is designed, which realizes the up-film boat-bottom-shaped transplanting technology. (1) For boat-shaped transplanting to occur, an arc-shaped clamping mechanism was created. The positioning cam and transposition mechanism were used to change the rotating center point of the clamping rod so that the junction point of the clamping rod and the mulch film was always maintained in the same spot. (2) A dislocation mechanism was designed to stagger the trajectory of the grasping mechanism that was put into the soil and the trajectory of the process of it as it came out of the soil. (3) Field tests were used to verify the machine’s working performance at various speeds, and the operating parameters were optimized.

2. Materials and Methods

2.1. Agronomic Requirements

The springtime transplanting of sweet potatoes is often performed with seedlings that are longer than 250 mm and that are naked. As illustrated in Figure 1, the boat-bottom-shaped sweet potato must be film mulched before the transplanting takes place. After the transplanting process, the root depth of the seedlings (RDS) should be between 20 mm and 30 mm, the node depth in the middle of the seedling (NDMS) should be between 40 mm and 60 mm, and the stalk length that is in the soil (SLS) should be between 180 mm and 220 mm. The range of the plant spacing should be from 180 mm to 300 mm [22].

2.2. Overall Structure and Working Principle

To meet the agronomic requirements in Section 2.1, an up-film transplanting device was designed to achieve boat-bottom-shaped sweet potato transplants. As shown in Figure 2, Figure 2a shows the structure of the whole machine, including the seedling conveying device and the transplanting device. The seedling conveying device follows the previous research results [16]. Figure 2b is the structure diagram of the transplanting device, which is also the object of this study. The transplanting apparatus is made up of the clamping mechanism, the positioning cam, the transposition mechanism, and the transmission system. At the rotation center point of the clamping mechanism is a cam for managing the opening and closing of the arc-shaped clamping lever. Accordingly, the positioning cam and the transposition mechanism jointly constrain the position of the rotation center point of the clamping mechanism. After clamping the seedling, the clamping mechanism enters the soil by rotating counterclockwise. In the process of the clamping mechanism entering the soil, the function of the positioning cam is to eliminate the horizontal displacement of the clamping mechanism in the forward direction that is caused by the forward speed of the implement. In order to stagger the movement trajectory of the clamping mechanism leaving the soil and entering the soil, which can prevent the clamping mechanism from taking the seedling out of soil when it is unearthed, the clamping mechanism is lifted a certain distance through the transposition mechanism so that the clamping mechanism leaves the soil with a movement trajectory that is above the trajectory of movement when it is entering the soil. The clamping mechanism leaves the soil by turning clockwise after releasing the seedling. During the process of the clamping mechanism leaving the soil, the effect of the positioning cam is divided into two parts. On the one hand, this is conducted to eliminate the horizontal displacement in the advancing direction of the clamping mechanism which is caused by the advancing speed of the machine, and on the other hand, this is conducted to adjust the intersection of the clamping mechanism and the mulch film during the ascent process, which is specifically explained as eliminating the distance difference between the intersection and the soil entry position. After the clamping mechanism completely leaves the soil, the positioning cam pushes the clamping mechanism forward, and the pushing distance is equal to the forward displacement of the transplanter within a period of time, which is the length of time from which the clamping mechanism enters soil to when it leaves soil. When the clamping mechanism is pushed back to the predetermined position, the preparation for gripping the next seedling begins.

In the above-mentioned movement process, the description of the movement mode of the control mechanism is as follows. The commutation gear set 2 controls the rotation process of the clamping mechanism. The reversing gear set 1 controls the up and down movement process of the transposition mechanism. However, in order to maintain the stable transmission of the mechanism and ensure the accuracy of the movement trajectory of the clamping mechanism, the positioning cam and its rotating shaft, push rod, and gear set 2 are all installed on the plate that can slide up and down, and the whole up and down movement of the sliding plate is controlled by changing to gear set 1.

2.3. Design of the Clamping Mechanism

2.3.1. Structural Design of Clamping Mechanism

In order to make sure that the damage that the clamping mechanism causes to the mulch film only occurs in a specific position, a clamping mechanism was designed in which the arc-shaped clamping rod moves in a reciprocating manner to it; this position is where the clamping mechanism enters the mulch film, and the movement trajectory of the end of the clamping mechanism in the soil can meet the agronomic needs of sweet potato’s boat-bottom-shaped transplanting device, such as shown in Figure 3. According to the agronomic requirements that are described in Section 2.1, the following agronomic parameters were used in the design of the mechanism: the theoretical submerged depth of the nodes in the middle of the seedling was 50 mm, while the theoretical depth of the seedling’s root was 25 mm. The constraint condition for the radius of the arc-shaped gripping rod was given by Equation (1). Let x represent the radius of the rotation of the gripping mechanism and set α + β represent the angle that is occupied by the arc that is formed when the sweet potato seedlings are buried in the soil. The calculation indicates that the radius was 130 mm, α = 52°, and β = 36°.

$$2\pi x.\frac{\arccos \frac{x^2-75x+1250}{x^2-50x}+\arccos \frac{x-50}{x}}{360}=200$$

(1)

As shown in Figure 4, the gripping mechanism reciprocates around the center of the handle 9. The rotation of the cam can control the iron ring 5 to slide back and forth along the concave slideway (part 6) through to part 7. The iron ring (5) pulls the two L rods so that they move. The L rod and the gripping rod are connected by a rotating pair so that the opening and closing movement of the two gripping rods can be controlled.

The opening and closing process of the gripping mechanism is shown in the schematic diagram of Figure 5, in which it can be known that the L rod realizes the opening and closing movement of the gripping mechanism, which is by controlling the rotation of the gripping rod. The angle of rotation of the gripper rod is ∠3, which can be expressed as Equation (2):

$$\angle 3=\arccos \frac{A_1{O}_1^2+{(\frac{A_1{O}_1\cos \angle 1-A_{1}D}{\cos \angle 1})}^2-{(A_{2}D+A_{1}D\tan \angle 1)}^2}{2A_2{O}_{1.}\frac{A_1{O}_1\cos \angle 1-A_{1}D}{\cos \angle 1}}$$

(2)

The value difference between point A₁ and point A₂ on the y axis is:

$$A_{1}D=A_1{C}_1\cos \angle 4-A_2{C}_2\cos \angle 5+C_1{C}_2$$

(3)

$$A_{1}D=A_1{O}_1\cos \angle 1-A_2{O}_1\cos \angle 2$$

(4)

By combining with ∠2 = ∠1 + ∠3, it can be known that:

$$C_1{C}_1=A_1{O}_1\cos \angle 1-A_2{O}_1\cos \angle 2-A_1{C}_1\cos \angle 4-A_2{C}_2\cos \angle 5$$

(5)

We brought Equation (2) into Equation (5) to get the constraints of C₁C₂ on ∠3.

It can be seen from Figure 6 that the maximum value of the tip opening of the gripper rod should be:

$$L_d=2\frac{l_2-l_1}{l_2}.r_1.\tan \frac{\angle 3}{2}$$

(6)

Note: L_d is the maximum size of the tip opening of the clamping rods.

2.3.2. Cam Design of the Clamping Mechanism

The cam controls the gripping mechanism’s opening and closing movements. According to the Formula (1), the angle of the sweet potato seedlings which form the arc in the soil is α + β = 88°. With reference to the working process of the gripping mechanism that is depicted in Figure 7, it is possible to determine the working area of the gripping mechanism for grasping the seedlings, as well as the key time nodes from opening to closing and from closing to opening. As shown in Figure 8, one rotation of the cam according to a-b-c-d-a is a working cycle. The height of the cam lift is the distance of lc.

The workflow of the cam is described below. As shown in Figure 8, the clamping mechanism quickly closes when the cam operates at point a, and it remains closed until the cam reaches point b. In the ab working stage of the cam, the gripping mechanism completes the process of grasping the sweet potato seedlings and transplanting them into a boat-shaped configuration. When the cam operates at point c, the clamping mechanism is re-clamped. In order to prevent the lateral tearing of the mulch, which is caused by the clamping rod, it is necessary to keep the clamping mechanism closed prior to it leaving the mulch. After the clamping mechanism completes the preceding steps, it enters a state of preparation before clamping the next sweet potato seedling, and it must be reopened. Therefore, when the cam passes through point d, the gripping rod opens, and when the cam rotates to point a, the clamping rods closes and picks up the next sweet potato seedling.

2.3.3. Design of Commutation Gear Set 1

A commutation gear set, which is depicted in Figure 9, was built in order to implement the forward and reverse rotation of the grasping mechanism that is described in Section 2.3.2’s Figure 5. The entire commutation gear set is driven by the rotation of sprocket 1. Sprocket 1 drives sprocket 2 to rotate through the chain. Sprocket 2 drives gear 3 and gear 4 to rotate at the same angular speed. Gear 5 and gear 6 rotate at the same angular velocity. Gear 3 meshes with gear 5. Gear 4 and gear 6 are gears that have half the number of teeth missing in them, and alternately, they mesh with gear 7 to drive gear 7 to rotate forward and reverse periodically. Finally, the sprocket 10 is driven to rotate forward and reverse through gear 8 and gear 9. Sprocket 10 transmits the power to the sprocket that is fixedly connected to the rotation center of the clamping mechanism so as to realize the forward and reverse rotation of the clamping mechanism.

The residual gear plays an important role in the commutation drive system. However, it is precisely because of the existence of the residual gear that its transmission characteristics cannot be expressed with a traditional transmission ratio. Therefore, we set out from the indexing arc degree that is occupied by the teeth in the residual gear to describe its transmission relationship. In Figure 9, the addendum circle diameters of gear 3, gear 4, gear 5, gear 6, and gear 7 are equal. However, the meshing of the gears is constrained by the diameter of the dividing circle. Therefore, the diameter of the dividing circle should be taken into consideration when one is designing the number of teeth of the residual gear. The angle of the tooth distribution in the residual gear follows the calculation rules of Formula (7) and (8).

$$A_{teeth}=\pi -\psi$$

(7)

$$\psi =2\arccos \frac{d}{D}$$

(8)

Notes: A_teeth is the angle that is occupied by the toothed part of the residual gear. d is the diameter of the indexing circle, and D is the diameter of the addendum circle.

Notes: In Figure 9, sprocket 1 is assembled on the rotating shaft of the positioning cam, and sprocket 2 and sprocket 10 are assembled on the sliding plate through the rotating shaft. Sprocket 2 and gears 3 and 4 rotate at the same angular velocity; gears 5 and 6 rotate at the same angular velocity; gears 7 and 8 rotate at the same angular velocity; gear 9 and sprocket 10 rotate at the same angular velocity. In Figure 10, the shaded part represents the part with the teeth.

2.4. Structural Design of the Transposition Mechanism

After the clamping mechanism inserts the sweet potato seedlings into the soil layer and completes the boat-shaped transplanting process, it must return and begin the transplanting cycle for the next seedling. Nevertheless, if the gripping mechanism returns according to the path that is taken during the transplanting process, then the gripping rod’s movement path will coincide with the position of the sweet potato seedlings in the soil, and the sweet potato seedlings will be extracted from the soil due to the frictional force of the gripping rod. To solve this problem, a transposition mechanism that is shown in Figure 11 was designed. The working phase of the mechanism can be divided into two parts: dislocation and reset. The dislocation movement is the stage of the clamping mechanism from the completion of the bottom-shaped transplanting process to the completion of the filming process, and the vertical height of the rotation center of the clamping mechanism is adjusted. The reset movement is to reset the rotation center of the gripping mechanism to its original vertical height after the gripping rod leaves the film. To realize the dislocation movement, the transposition mechanism must control the movement of the positioning cam, the push rod, and the clamping mechanism as a whole since the positioning cam controls the horizontal movement of the clamping mechanism’s rotation center position via the push rod. Reversing gear set 1 and the positioning cam that control the rotation of the clamping mechanism are connected to the sliding plate via the rotating shaft, and the push rod is connected to the slidable rack plate via the slider in order to realize the overall movement of the three parts. By controlling how the sliding frame plate moves, it is possible to ensure that the three parts move as a whole. Therefore, the gears that are based on the Archimedes spiral and commutation gear set 2 are designed to control the movement of the slidable board.

2.4.1. Design of Gears Based on Archimedes Spirals

The gear and the Archimedes spiral slide are both the components of the gear that are based on the Archimedes spiral, in which the up and down movement of the sliding rack 1 cause the gear to rotate, and the meshing of the Archimedes spiral slide and sliding rack 2, the helical slideway, and the rotation of the fixed gear maintain a synchronous rotation. As illustrated in Figure 12, the Archimedes spiral slideway and the slideway rack 2 are connected by a slider, one end of which is fixed to the frame and the other end of which is connected to the center of the Archimedes spiral slideway by a rotating pin. Thus, the rotation of the Archimedes spiral slideway can be converted into the up and down movement of the sliding rack 2, and since the sliding rack 2 is fixedly connected to the sliding plate, the up and down movement of the sliding plate is achieved.

In order to prevent the mulch film from being cut when the gear mechanism that is based on the Archimedes helix is operating in conjunction with seedling head immersion depth of 25 mm that is noted in Section 2.3.1, the mechanism is designed to raise the planting mechanism by 15 mm. This is how the agency was created.

The Cartesian coordinate equation of the original Archimedes spiral is:

$$\left\{\begin{array}{l}r=a(1+t)\\ x=r.\cos (t.360)\\ y=r.\sin (t.360)\\ z=0\end{array}\right.$$

(9)

Note: a is the radius at the initial moment, and t is the working time.

The working principle of the Archimedes screw mechanism reveals that it does not operate continuously, so the parameter t in the Formula (9) represents a nonlinear change value. The modified helix equation is shown in Formula (10), and the change interval and change trend of f(t) are shown in Formula (11). In order to reduce the variation coefficient of the plant spacing, the rotary encoder is used to monitor the rotation speed of the ground wheel, and the rotation speed of the ground wheel is used to guide the operation speed of the planting mechanism. Because of this, the forward speed of the machine has the largest effect on the speed at which it can transplant. The time T when the cam rotates 360° is chosen to determine a specific working cycle to describe the time when the transplanter completes the process of transplanting a seedling. Despite the fact that the value of T varies with the forward speed of the machine, it is always equal to one rotation of the cam. In Section 2.3.3, the entire process of moving the sweet potato seedlings with the gripping rod is described in detail, and this process allows one to determine the movement status of the dislocation device during a single working cycle. In Formula (11), one working cycle of the dislocation device is divided into five stages:

(1) The static state of the transposition device is described in this stage. In this stage, the clamping mechanism completes the movement process from clamping the sweet potato seedlings to completely inserting the sweet potato seedlings into the soil. The clamping mechanism does not need to move in the vertical direction, so the transposition device is not working.

(2) A consistent ascent is described in this stage. After completing the first stage of movement, the gripper loosens the sweet potato seedlings; therefore, the gripper’s task during this stage is to leave the mulch without expanding the film opening. The dislocation device raises the planter as a whole in order to separate the trajectory from the transplanting trajectory. Through the rack and pinion structure, the upward movement is made to be uniform so that it can be controlled with greater stability.

(3) This stage describes the stationary motion. In the previous stage, the track dislocation is accomplished by raising the height of the clamping mechanism’s rotation center. However, at the conclusion of the previous stage, the clamping rod had not completely separated from the mulch film so the task of the dislocation device in this stage is to wait for the gripper rod to fully separate from the mulch.

(4) This stage describes the uniform descent; the distance of the descending path is identical to the distance of the ascending path in the second stage. In this phase, the gripping rod has been separated from the mulch, and the dislocation device must now lower the rotation center point of the gripping mechanism to its initial height and enter the work preparation state in order to grip the next seedling.

(5) This stage describes the stationary motion. The fifth stage is an extension of the fourth stage because the success rate of the gripping rod will decrease if the seedlings are harvested immediately after the fourth stage. Therefore, the fifth design stage is performed to ensure that the gripping rod can eliminate the movement interference that is caused by the dislocation mechanism’s operation when it is gripping the seedlings.

$$r=a+f(t)$$

(10)

$$f(t)=\left\{\begin{array}{lll}0\hfill & 0\le t\le \frac{126°}{360°}T\hfill & \begin{array}{cc}step& 1\end{array}\hfill \\ 180\frac{t-\frac{126°}{360°}T}{T}\hfill & \frac{126°}{360°}T\le t\le \frac{156°}{360°}T\hfill & \begin{array}{cc}step& 2\end{array}\hfill \\ 15\hfill & \frac{156°}{360°}T\le t\le \frac{230°}{360°}T\hfill & \begin{array}{cc}step& 3\end{array}\hfill \\ 15-180\frac{t-\frac{230°}{360°}T}{T}\hfill & \frac{230°}{360°}T\le t\le \frac{260°}{360°}T\hfill & \begin{array}{cc}step& 4\end{array}\hfill \\ 0\hfill & \frac{260°}{360°}T\le t\le T\hfill & \begin{array}{cc}step& 5\end{array}\hfill \end{array}\right.$$

(11)

2.4.2. Design of Commutation Gear Set 2

To implement the intermittent motion of the stages in Section 2.4.1, “Stationary-Up-Stationary-Descent-Stationary,” commutation gear set 2, which is depicted in Figure 13, is utilized. Three sets of gears, gear 1 and gear 2, residual gear 1 and gear 3, gear 4 and residual gear 2, rotate at the same speed. Because gear 3 is fixed on the power shaft, its rotation supplies power to the entire gear set. Gears 3 and 4 mesh. Gear 2 realizes the periodic motion of “stationary-forward rotation-stationary-reverse rotation-stationary” due to the alternating meshing of residual gear 1 and residual gear 2.

The working process of the previously described commutation gear set 2 reveals that gear 1 pushes the sliding rack upward by meshing with sliding rack 1. According to Formula (11), in the meshing motion of residual gear 1 and gear 2, the rising distance of the vertical rack is determined by the rotation angle of gear 2. The distance determines the rotation angle of the Archimedes spiral slide, which when it is combined with Formula (10), determines the height of the dislocation device. Consequently, the tooth distribution of the residual gear is essential for achieving the previously mentioned periodic motion.

Figure 14a demonstrates that residual gear 1 begins to mesh with gear 2, thus corresponding to step 2 of Formula (11). Figure 14b depicts the position where gear 2 is rotated to the halfway position after being propelled forward by residual gear 1. Figure 14c demonstrates that residual gear 2 begins to mesh with gear 2, thus corresponding to step 4 of Formula (11). Therefore, γ is the sum of the angles of the working stages of steps 2 and 3, δ is half of the angles of steps 2 and 3, and ε is the angle of the working stage of step 3. From Equation (11), we can obtain: γ = 104°, δ = 89°, and ε = 74°.

2.5. Design of Positioning Cam

The purpose of the positioning cam is to control the position at which the positioning cam intersects the gripping rod with the mulch film during one working cycle. The analysis in Section 2.4.2 consists of the five stages of the transposition mechanism’s motion. During the movement, the clamping rod will cause additional damage to the mulch due to the change in the movement state. To address this issue, a positioning cam is created to adjust the gripping rod’s position. The primary objective is to adjust the position of the gripping rod’s rotation center so that contact with the mulch film is always maintained at the film-breaking hole upon its entry into the mulch film. One may find this adjustment point by using the mulch as a reference plane and observing the intersection of the gripper bar with this plane.

In conjunction with the working stages of the transposition mechanism, the positioning cam’s edge contour curve is divided into six stages. For greater clarity, the positioning cam’s functions are depicted in Figure 15.

Because the operating speed of the planting mechanism is determined by the forward speed of the machine and the plant spacing, the plant spacing will be an important parameter that one should consider when they are designing the contour equation of the positioning cam edge. The plant spacing is established to be at 240 mm. Both the third and fourth stages involve numerous variables. These variables are converted to the rotation angle of the positioning cam for a more precise expression to be produced. The following formula, Formula (12), illustrates the contour curve equation of the six-segment edge of the positioning cam, and the design principle is as follows:

Stage 1: During which the gripping rod grasps the seedlings and enters the soil. As the gripping rod has no contact with the mulch during this stage’s movement, it is not necessary to eliminate the horizontal linear speed of the gripping rod’s rotation center by positioning the cam. Therefore, the initial edge contour equation is constant.

Stage 2: The positioning of the cam needs to balance the center of the rotation of the arc gripper lever, which is affected by the forward speed of the implement. In this phase, the work process for the curved gripping rod begins with its entry into the ground, and this task continues until its completes the path of the bottom-shaped trajectory. Consequently, it is necessary to position the cam to eliminate the horizontal movement speed of the gripping rod’s rotation center so that the arc-shaped gripping rod rotates about the fixed circle center. So, the edge contour function of the second stage is a linear function that stops the implement from moving forward.

Stage 3: The positioning of the cam needs to balance the two aspects of speed: 1. The horizontal advance speed of the machine; 2. The offset of the contact position between the gripper rod and the mulch film when the gripper rod rotates under the influence of the horizontal advance speed and the vertical rise of the transposition device. Therefore, the edge contour function of the third stage must add a variable that is based on the second stage: when the arc-shaped gripping rod rises with the transposition device, the length value between the gripping rod’s rotation center and the film-breaking point changes (for more precise calculation, the perforating hole myopia as a point).

Stage 4: At this stage, the transposition mechanism has completed the process of pulling up the rotation center point of the gripping mechanism, so it is only necessary for it to balance the forward speed of the implement. The working essence of this stage is the same as that of the second stage; it relies on the positioning cam to eliminate the horizontal linear velocity that is caused by the advancing of the implement to the rotation center of the gripping rod.

Stage 5: The positioning cam resets the arc-shaped gripping rod by pushing it back to a position in which the machine moves normally. This stage’s objective is to compensate for the lack of horizontal displacement that is caused by the restricted movement between the second and fourth stages.

Stage 6: After the first five stages, the transplanting process and the resetting of the arc-shaped gripping rod have been performed within one working cycle of the cam. The purpose of this stage is to make the arc-shaped gripping rod enter the ready state for it to grip the seedlings.

$$f(\phi )=\left\{\begin{array}{llll}\frac{360-38}{360}\times 240\hfill & 0\le \phi \le 38\hfill & stage\hfill & 1\hfill \\ f(38)-\frac{f(38)}{360-38}\times (\phi -38)\hfill & 38\le \phi \le 126\hfill & stage\hfill & 2\hfill \\ f(38)-\frac{f(38)}{360-38}\times (\phi -38)+\sqrt{{130}^2-{80}^2}-\sqrt{{130}^2-{\left[80+0.5(\phi -126)\right]}^2}\hfill & 126\le \phi \le 156\hfill & stage\hfill & 3\hfill \\ f(156)-\frac{f(38)}{360-38}\times (\phi -156)\hfill & 156\le \phi \le 196\hfill & stage\hfill & 4\hfill \\ \frac{f(38)-f(196)}{330-196}.(\phi -196)+f(196)\hfill & 196\le \phi \le 330\hfill & stage\hfill & 5\hfill \\ \frac{360-38}{360}\times 240\hfill & 330\le \phi \le 360\hfill & stage\hfill & 6\hfill \end{array}\right.$$

(12)

Figure 16 depicts the motion trajectories of the six stages of the arc-shaped clamping rods in Formula (12).

2.6. Design of Plant Spacing Control System

To guarantee that the membrane rupture hole is small, a plant spacing control system that is based on the measurement of the rotary encoder speed is designed. The system uses PLC as its primary controller, and it adjusts the rotational speed of the power shaft in real time as it is based on the forward speed data that are collected by the rotary encoder in order to achieve the real-time matching of the transplanting rate and the forward speed of the implement.

2.6.1. Design of the Forward Speed Monitoring Scheme of the Implement

Detecting and ensuring the consistency of the ground wheel speed and the transplanting rate of the transplanting device is essential to achieve the control of the system. To function as the speed detection device, an Omron ABZ three-phase photoelectric rotary encoder, is selected, and the ground wheel and DC brushless motor are connected via a chain. As depicted in Figure 17, rotary encoder 2 measures the rotational speed of the ground wheel to determine the forward speed of the implement, while rotary encoder 1 measures the rotational speed of the motor.

In this study, the M method was chosen to measure the speed of the transplanter’s ground wheel and DC brushless motor. The specific principle is to calculate the current forward speed of the machine and the motor speed by accumulating the total number of pulses that are measured by the encoder during the time interval. Equations (13) and (14) display the formulas for solving the traveling speed and the motor speed, respectively.

$$v=\frac{\pi d{M}_1}{P_1{T}_g}\times 6000$$

(13)

$$r=\frac{M_2}{P_2{T}_g}\times 60$$

(14)

Notes: v is the travel speed that is measured by the encoder (m/min), M is the total number of pulses that are measured in the time interval, P is the number of pulses that are sent by the encoder per revolution, T_g is the selected time period (s), d is the diameter of the ground wheel of the planter or tractor (cm), and r is the motor speed r/min.

2.6.2. System Software Design

Measurement, comparison, and implementation are the three fundamental steps in system feedback theory adjustment. The measurement step is taken to gather the actual value of a controlled object and compare it to the intended value of it. We used the system’s deviation from the intended values to regulate and adjust the system’s reaction [23]. Figure 18 depicts the basic workings of the control system.

In PID control, e(t) is the difference between the theoretical speed r(t) and the actual speed c(t), and u(t) is the output of the PID controller and the input signal of the controlled object. The analog PID controller’s control law is as follows:

$$e(t)=r(t)-c(t)$$

(15)

$$u(t)=k_p\left(e(t)+\frac{1}{T_I}{\displaystyle {\int }_0^{t}e(t)dt+T_D\frac{de(t)}{dt}}\right)+u_0$$

(16)

Notes: k_p is proportional coefficient; T_I is integral time constant; T_D and u₀ are differential time constant and control constant, respectively.

Since the sampling control is used to operate the system, the discrete PID formulation is as follows:

$$u_k=k_p\left[e_k+\frac{T}{T_I}{\displaystyle \sum _{j=0}^K{e}_j+\frac{T_D}{T}(e_k-e_{k-1)}}\right]+u_0$$

(17)

The brushless DC motor speed is controlled using an incremental PID system rather than a position PID system because it decreases system offset that is caused by the accumulated error. As a part of the PID control algorithm, the control quantity’s increment Δu_k must be calculated.

$$\begin{array}{l}\Delta u_k=u_k-u_{k-1}=k_p\left[e_k-e_{k-1}+\frac{T}{T_I}{e}_k+\frac{T_D}{T}(e_k-2e_{k-1}+e_{k-2})\right]=\\ k_p\left[(1+\frac{T}{T_I}+\frac{T_D}{T})e_k-K_p(1+2\frac{T_D}{T})e_{k-1}+k_p\frac{T_D}{T}{e}_{k-2}\right]=A{e}_k+B{e}_{k-1}+C{e}_{k-2}\end{array}$$

(18)

If you take three measurements before and after the process is performed, the control increment can be determined. The rotary encoder 2 monitors the vehicle speed in real time and calculates the theoretical motor speed that is based on the function which is related to the vehicle speed and the control motor speed when the sweet potato transplanter is operating. In order to move the motor, a voltage analog signal is outputted by the controller (corresponding to a value of 0–10 V). turn. The system error is measured by subtracting the motor’s actual speed from its theoretical speed, and the control concept is depicted in Figure 19.

Figure 20 depicts the control flow. The motor speed measurement feedback device returns the current motor speed to the controller after completing a control cycle, and the difference calculation with the theoretical motor speed is then carried out once more. The controller continues to make incremental PID adjustments to the motor when the error exceeds the permitted range. For better system stability to achieve values that are near the goal value, the default speed adjustment is finished if the error is less than 0.05 km/h; if it is larger than 0.05 km/h, the program control cycle will continue.

2.7. Conditions and Methods of Field Trials

A field test was carried out in order to verify the reliability and stability of the operation of the above-mentioned design agency. The test site was carried out in the test field of Shandong Huorong Agricultural Science and Technology Development Co., Ltd (Weifang City, Shandong Province, China). As shown in Figure 21. The soil type was sandy loam. Before the experiment was performed, we sprayed water on the experimental field to increase the soil moisture content so that the soil moisture content reached 15% (error 1%), and then, we used the rotary tiller to perform rough rotary tillage, and then, we used the ridge machine to raise the ridge so that the ridge height was 300 mm. The width of the upper ridge was 300 mm, and the width of the bottom ridge was 800 mm. As soon as the ridge was raised, it was pressed flat and covered with a film to ensure that the top surface was flat. This was performed to prevent the test accuracy from being reduced as a result of excessive ridge height error. Considering that the plant spacing in the design of the transplanting device was 240 mm and the sweet potato compound transplanting machine group standard (T/CAAMM 52-2020), the minimum transplanting speed was 35 plants per minute, and the maximum artificial seedling speed was 60 plants/min [22]. The interval between 35 plants/min and 60 plants/min was equally divided into 35 plants/min, 40 plants/min, 45 plants/min, 50 plants/min, and 60 plants/min. According to Formula (13), it can be seen that the forward speeds of the tractor were 0.14 m/s, 0.16 m/s, 0.18 m/s, 0.20 m/s, 0.22 m/s, and 0.24 m/s, respectively. Six distinct groups of experiments were conducted, and each group experiment was repeated three times. Figure 22 shows the effect after transplanting. Due to the unstable speed of the tractor during the starting and stopping phases, 310 seedlings were transplanted in each experimental group, but the first and last five seedlings did not fall within the measurement range so only the middle 300 seedlings were evaluated. The test indexes were divided into two aspects: the seedling index and the membrane hole index. The index of the seedlings included three elements: the qualified rate of the depth of the middle of the seedling; the qualified rate of the base of the seedling; the qualified rate of the length of the stem of the seedling. The membrane hole indicators included three elements: hole spacing, membrane hole length, and the change rate of the membrane hole length.

$$v=\frac{d.p}{1000t}$$

(19)

Notes: v is the forward speed of the tractor, m/s; d is the plant spacing, 240 mm; p is the transplanting rate, plant/min; t is the time, 60 s.

(1)

This section concerns the shape and length of the hole in the membrane.

Numerous factors, such as the mulch film’s elasticity and plasticity, the slippage of the ground wheel, and the variation in the motor’s rotation response time will cause the film holes to assume various shapes. Consequently, it is necessary to define a measurement method to determine the length of the membrane pores, as depicted in Figure 22, which shows the measurement methods for the membrane pores of different shapes. The length of the pores are measured along their longest axis, regardless of the shape of the pores. d₁ and d₂ in Figure 23 serve as plant spacing measurements.

The formula for calculating the rate of change in membrane pore length is:

$$J=\frac{\left|\left.l-L\right|\right.}{L}\times 100\%$$

(20)

Notes: l represents the actual pore length, mm; L represents the theoretical pore length, mm.

(2)

This section concerns the node depth in the middle of the seedling that is buried in the soil (NDMS).

In the statistical test data, the value of the deepest submerged depth in the middle of the seedlings of each group of tests is the average of 300 measurements, and the value of each measurement must fall within the range of 50 mm to 70 mm in order for them to be qualified. The qualified rate Q₁, is calculated as follows:

$$Q_1=\frac{M_1}{M}\times 100\%$$

(21)

Notes: M₁ is the number of qualified plants in the test sample, per plant; M is the total number of plants in the test sample, per plant; Q₁ is the qualified rate of node depth in the middle of the seedling (QRNDMS), %.

(3)

This section concerns the root depths of seedlings that are buried into soil (RDS).

If the measured value of the submerged depth of the seedling root falls between 20 mm and 30 mm, then it is qualified, and the qualified rate Q₂ is calculated as follows:

$$Q_2=\frac{M_2}{M}\times 100\%$$

(22)

Notes: M₂ is the number of qualified plants in the test sample, strain; M is the total number of plants in the test sample, per plant; Q₂ is the qualified rate of the root depths of the seedlings that are buried into soil (QRRDS), %.

(4)

This section concerns the stalk length in the soil (SLS).

The measured value of the length of the seedling that is in the soil is qualified within the range of 180–220 mm, and the calculation formula of the qualified rate Q₃ is:

$$Q_3=\frac{M_3}{M}\times 100\%$$

(23)

Notes: M₃ is the number of qualified plants for the determination of the sample, strain; M is the total number of plants for the determination of the sample, per plant; Q₃ is the qualified rate of stalk length that is in the soil (QRSLS), %.

3. Results and Discussion

The field performance test was carried out on the sweet potato boat-bottom-shaped film transplanter in the above-mentioned manner, and the test results are shown in

Table 1. Transplantation and film-breaking performance test results.

Test Number	Forward Speed (m/s)	Seedling			Hole
		QRNDMS (%)	QRRDS (%)	QRSLS (%)	Hole Distance (mm)	Hole-Opening Diameter (mm)	Change Rate of Hole Length (%)
1	0.14	95.33%	94.00%	98.00%	239.12	39.25	1.88
2	0.14	95.67%	93.67%	97.33%	241.25	39.17	2.08
3	0.14	96.00%	94.33%	98.33%	240.61	38.97	2.58
Average value	0.14	95.67%	94.00%	97.89%	240.33	39.13	2.18
4	0.16	95.33%	94.33%	97.33%	241.09	36.91	7.73
5	0.16	94.33%	94.33%	96.67%	243.24	36.98	7.55
6	0.16	95.00%	93.33%	97.00%	239.38	37.14	7.15
Average value	0.16	94.89%	94.00%	97.00%	241.24	37.01	7.48
7	0.18	94.67%	93.33%	96.33%	241.53	37.15	7.13
8	0.18	94.33%	93.33%	96.67%	240.47	37.23	6.93
9	0.18	94.67%	94.00%	96.33%	244.19	36.85	7.88
Average value	0.18	94.56%	93.67%	96.44%	242.06	37.08	7.31
10	0.20	93.33%	93.00%	95.67%	245.17	39.29	1.78
11	0.20	92.33%	93.33%	95.33%	242.61	38.97	2.58
12	0.20	93.00%	93.00%	95.33%	243.32	39.03	2.43
Average value	0.20	92.89%	93.11%	95.44%	243.70	39.10	2.26
13	0.22	91.33%	92.33%	94.33%	243.98	40.49	1.23
14	0.22	90.67%	91.33%	94.00%	244.62	40.45	1.13
15	0.22	89.67%	91.67%	94.67%	244.75	39.68	0.8
Average value	0.22	90.56%	91.78%	94.33%	244.45	40.21	1.05
16	0.24	86.67%	89.67%	92.00%	246.43	42.39	5.98
17	0.24	86.00%	90.00%	91.33%	245.89	42.05	5.13
18	0.24	87.67%	90.67%	91.67%	243.65	41.87	4.68
Average value	0.24	86.78%	90.11%	91.67%	245.32	42.10	5.26

Note: Each group of tests includes three times. The bold part in the table is the average value of each group of tests.

.

As shown in

Table 2. Variance analysis.

Source	F Value	p Value
QRNDMS	98.169	<0.01 **
QRRDS	37.028	<0.01 **
QRSLS	133.704	<0.01 **
Hole Distance	5.384	<0.01 **
Hole-opening Diameter	176.332	<0.01 **
Change rate of hole length	124.425	<0.01 **

Note: ** expresses highly significant (p ≤ 0.01).

, the p value and F value of the test data were checked through the performance of a mathematical statistical analysis.

3.1. Results and Analysis of the Qualified Rate of Transplanting Sweet Potato Seedlings

In Figure 24, the QRNDMS, the QRRDS, and the QRSLS are illustrated. The figure shows that as the machine’s forward speed increases, the pass rates of the three indicators decrease.

(1) The QRNDMS decreases with increasing forward velocity in the range of 0.14 m/s to 0.18 m/s, although the trend is not statistically significant. This index indicates that the implement’s performance is relatively stable and satisfactory in this forward speed range. When the machine tool’s forward speed is between 0.18 m/s and 0.24 m/s, the pass rate drops dramatically, with the pass rate falling to below 90% when the forward speed is 0.24 m/s.

The reason for this phenomenon having occurred in the test results is that increasing the forward speed of the machine will significantly disturb the soil on the upper portion of the seedlings. To elaborate, the transplanting frequency increases as the forward speed of the implement increases, and the increase that occurs in transplanting frequency causes an increase in soil disturbance after the clamping mechanism has been inserted into the soil. The bottom shape of the stalk in the middle of the seedling is bowed downward, which occurs due to the pressure of the upper soil on it. In an ideal situation, it is believed that the pressure of the soil on the seedling will cause the seedling to bend along the trajectory of the movement of the clamping mechanism’s end. However, the disturbance of the soil by the gripping mechanism will soften the soil on the upper portion of the seedlings, and after the soil is discarded, the upper portion of the seedlings will be devoid of soil. Thus, the culm is not bent to the theoretically calculated depth.

The research of Hu et al. [24] confirms the veracity of the aforementioned phenomenon. According to their research, the actual transplanting depth would be less than the theoretical design value. When the transplanting depth is used as the test factor and there is a smaller value for it that is within the qualified depth range, then the qualified depth rate will be lower than the transplanting depth is, whereas when there is a larger value for it that is within the qualified depth range, then the pass rate will increase as the transplanting depth increases. Yu et al. [25] also confirmed this result with their research. As the transplanting depth increased, the transplanting qualification rate exhibited an upward trend.

(2) Although the forward speed of the QRRDS random tool has slowed, the downward trend is not evident, and the gap between the highest and lowest pass rates is only 2.89 percentage points (this result can be obtained from Table 1).

The operation of the planting mechanism determines the cause of this occurrence. The position of the seedling base in the soil is recorded at the end of the movement of the gripping mechanism (the end of the movement in the soil) in one transplanting cycle, despite the fact that the change in the forward speed of the implement will disturb the soil. Therefore, the soil disturbance at the position where the seedling’s base is located due to the gripping mechanism is minimal, and the soil disturbance intensity is obviously less than that at the position where the seedling’s stem is located. This portion of the pressure that is exerted by the upper mulch on the soil will be relatively small. Additionally, because of the elastoplasticity of the mulch film itself (the mulch is tightly covered on the ridge and the ridge will be covered with soil to compact the mulch), there will be a certain amount of pressure on the soil beneath the film, and this portion of the pressure will reduce the amount of arched soil that is caused by disturbance.

(3) There are two phenomena which are involved in the evolution of the QRSLS. First, it decreases as the forward speed of the tool increases. The degree of this decrease is relatively stable between 0.14 m/s and 0.22 m/s, and the rate of this decrease increases significantly between 0.22 m/s and 0.24 m/s; however, the entire testing procedure is inconclusive. This indicator’s pass rate remains relatively high. At six different forward speeds, the qualified rate of the seedling length in the soil was greater than those of the other two indices.

There are two causes for this occurrence. First,

Table 3. Comparison of design value and qualified range.

	Test Index	RDS (mm)	NDMS (mm)	SLS (mm)
Value and Range
Qualified range		20–30	40–60	180–220
theoretical value		25	50	200

compares the design values and the qualified ranges of the three indicators for the sweet potato seedlings which were transplanted into the boat-bottom-shaped film transplanter. The table demonstrates that different error margins are required for the three transplantation indicators. To be qualified, the RDS requires that the working error within this index is within 5 mm, the NDMS requires that the working error within this index is within 10 mm, and the SLS requires that the working error within this index is within 20 mm. Consequently, it is evident that the SLS meets the requirements with relative ease. Second, when the disturbance that is caused to the soil is excessive, thus causing the NDMS to exceed the qualified range, the impact that this has on the length of the seedlings in the soil is greater, which also explains the qualified rate of the machine’s advancing speed that is within the range of 0.22–0.24 m/s. This is the reason for the sharp decline that occurs.

Although there are no studies in the literature that directly addressing this indicator, it is evident from the above-mentioned analysis that the transplanting depth is crucial for influencing the qualified rate of this indicator. Zhang et al. [26] demonstrate that there is a correlation between the qualified rate of transplanting depth and the theoretical transplanting depth. Within the qualified range of the theoretical depth, the test results show that the qualified rate of the transplanting depth is not as good when the depth value is small when it is compared to when the depth value is large.

(4) The analysis of the three test indices after the sweet potato seedlings have been buried in the soil demonstrates that the rate of the changes of the three indices is not significant under different forward machine speeds. With the exception of the QRNDMS at a forward speed of 0.24 m/s (86.78%), the pass rates of the other factors at each test level are all greater than 90%. Within the range of 0.14 m/s to 0.22 m/s, the operational performance is relatively good.

3.2. Results and Analysis of the Qualified Rate of Plastic Film Related Indicators

As depicted in Figure 25, the rules of the film hole spacing, the film hole length, and the film hole length change rate under various machine advance speeds are presented. According to the examination of the experimental phenomenon and relevant research literature, the causes of this occurrence are: (1) The slip rate of the ground wheel increases as the forward speed of the machine increases, thus causing the distance between the membrane holes to increase. (2) The plastic film is elastic and plastic, and its tensile speed correlates with its average elongation during a rupture. The following is the description of this process in detail.

3.2.1. The Variation Law of the Film Hole Spacing with the Increase in the Advancing Speed

The film hole spacing is greater than 240 mm, as depicted in Figure 24, which depicts the film hole spacing at various machine forward speeds. The distance between the membrane holes increases gradually as the advancing speed increases, and the trend of the increase is relatively stable. This phenomenon occurs because there is a slip rate during the advancement of the ground wheel. Zhang [27] studied the slip characteristics of the hanging cup transplanter and determined the following: when the traction speed is used as the test factor and the ground wheel slip rate is used as the index, the speed values are 0.21 m/s, 0.27 m/s, and 0.37 m/s, and the slip rates are 11.46 percent, 11.95 percent, and 12.44 percent, respectively. Thus, this study’s experimental phenomena and Zhang’s experimental phenomena are comparable. The slip rate calculation formula is shown in Equation (24). It can be deduced from ε> 0 that the actual travel distance exceeds the theoretical travel distance. Therefore, it can be concluded that as the velocity increases, so does the slip rate, and when the slip rate is positive, the plant spacing will increase. Comparing the plant spacing to the experimental index of this study is equivalent to comparing the membrane pore spacing to the plant spacing.

$$\epsilon =\frac{S_1-S_2}{S_1}\times 100\%$$

(24)

Notes: where ε is the slip rate of the ground wheel, %; S₁ is the actual driving distance of the ground wheel, mm; S₂ is the theoretical travel distance of the ground wheel, mm.

3.2.2. The Change Law of the Length of the Membrane Pores and Its Rate of Change with the Increase of the Advancing Speed

As shown in Figure 24, we have described the variation law of the film hole length as a function of the advancing speed of the implement, and the rate of change in the membrane pore length as a function of advancing velocity. The movement of the clamping mechanism will cause the mulching film to be pulled, and the direction of the pulling will extend the direction of the machine’s forward motion. Because the ground wheel slips, the relative displacement of the clamping rod’s rotation center occurs relative to the mulch film. However, as the forward velocity increases, the length of the membrane hole decreases, remains constant, and then increases. This phenomenon differs from the conclusion that is described in Section 3.2.1, which states that the occurrence of the phenomenon of the ground wheel slip increases with the increase in the forward speed. It is hypothesized that this phenomenon is the result of two factors: (1) the slip rate of the ground wheel increases as the advancing speed does, and (2) the elongation at the break of the mulch film increases as the stretching speed does. According to the three stages of the changes in the lengths of the membrane holes, the specific explanation for the aforementioned phenomenon is: When the distance between the membrane holes does not change significantly, in the range of 0.14 m/s to 0.16 m/s, under certain conditions (low slip rate), the elastoplasticity of the mulch can prevent the enlargement of the film pores which is caused by a shift in the plant spacing. Due to the ground wheel slipping, the point where the gripper rod meets the mulch film is moved. This causes the point to stretch in the direction of the machine’s forward movement. The elasticity of the mulch film makes up for the small movement of the point.

He [28] studied the average elongation of the tear of the mulch film by observing the tensile speed and the changing law of the elongation at the tear over different film-laying days. Since this study focuses on the mechanical properties of the mulching film during the transplanting process, the days during which the film laying takes place can be counted as 0, so only the results of He’s experiment when the days during which the film laying takes place are 0 are discussed here. The elongation of it increased from 203.03 to 210.9 percent at the tensile speeds of 30 mm/s and 50 mm/s. It is evident that the mulch film’s elongation rate will increase as its pulling speed increases. This also explains why the membrane hole length decreases as the implement’s forward velocity increases from 0.14 m/s to 0.18 m/s. The elongation rate of the mulch film can also explain why the length of the film hole is 40 mm less than the diameter of the clamping rod sleeve when the forward speed of the machine tool is between 0.14 m/s and 0.20 m/s. However, the length of the film hole increases as the forward speed of the machine increases from 0.20 m/s to 0.24 m/s. The reason for this phenomenon is that the actual plant spacing greatly exceeds the planned plant spacing so the elasticity and flexibility of the plastic film can no longer be utilized. The membrane hole is pulled by the gripper rod and then, its original state is restored. It is explained further that the length of the mulch film that is stretched by the clamping rod has exceeded the mulch film’s elastic deformation range. The average elongation at the tear is significantly affected by the tensile speed, and as the tensile speed increases, so does the average elongation at tear of the mulch film. These experimental outcomes are comparable to the outcomes of this study.

4. Conclusions

(1) According to the agronomic requirements of the up-film transplanting of sweet potato seedlings with a boat-bottom posture, the arc clamping mechanism has been designed. In order to avoid the lateral displacement of the clamping mechanism, which is caused by the forward speed, the positioning cam has been designed. In order to ensure that the movement track of the clamping mechanism does not coincide with the movement track of it entering the soil during the process of it leaving the soil, the displacement device has been designed.

(2) In the field experiment, six groups of experiments were conducted with the forward speed of the machine as the test factor. The results showed that the qualification rate of the three indexes of the seedlings is high, the length of membrane holes is small, and the distance between the membrane holes is stable, which meet the operation requirements. The change rate of the membrane pore length is lower than 7.48%, and this is within the acceptable range.

(3) Before the field test, the flatness of ridge surface was improved by the manual operation of the device, which was conducted to create a better working condition for the planting mechanism. Therefore, in order to put the designed machine into practical application, our next research work will design a matching ridging mechanism that will be attached on the machine.