Design and Test of Elastic Tooth Type Lateral Straw Clearing Roller Based on the Straw Clearing and Mulching No-Tillage Precision Planter

Abstract

Aiming at the problems of large soil disturbance, high power consumption and strong vibration during the operation of the 2BMFJ series straw clearing and mulching no-tillage precision planter with rigid teeth, an elastic tooth type lateral straw clearing roller was designed and the key parameters and values affecting the operation performance of the device were determined through theoretical analysis. Orthogonal test method was adopted to implement parameter combination improvement test with the length of tooth rod, the clearance of roller center from ground, the circumferential number of elastic teeth and the angular velocity of roller as test factors and straw clearing rate, power consumption and vibration intensity as performance evaluation indexes. The results showed that: all the factors had extremely significant effects on the straw clearing rate and power consumption performance evaluation indexes, except the clearance of roller center from ground had no significant effect on the vibration intensity performance evaluation indexes, the other factors have significant effects. Parameter optimization combination: At the planter forward speed of 7.2 km/h, the length of toothed rod was 270 mm, the clearance of roller center from ground was 360 mm, the circumferential number of elastic teeth was 8, the angular velocity of roller was 52 rad/s and the performance evaluation indexes were as follows: straw clearing rate was more than 90%, power consumption was less than 1.7 kW and vibration intensity was less than 85 m/s². Through the comparative test of the elastic tooth and rigid tooth type lateral straw clearing roller, there was no significant difference in the straw clearing rate between the two, but there were significant differences in the power consumption and vibration intensity. The elastic tooth type lateral straw cleaning roller reduced power consumption by 63.3% and vibration intensity by 43.2%.

1. Introduction

Straw mulching and no-tillage sowing are the cores of conservation tillage technology, which have the advantages of improving soil water storage and moisture retention, reducing wind and water erosion, increasing soil organic matter content, reducing soil disturbance, reducing operation procedures and reducing soil compaction [1,2,3]. 2BMFJ series straw clearing and mulching no-tillage precision planter adopts the principle of lateral “straw clearing and mulching” to realize the functions of no-tillage precision sowing and uniform straw surface coverage after sowing in one operation [4]. In the process of straw cleaning with rigid teeth structure, it is necessary to improve the straw clearing rate on the surface by increasing the depth of rigid teeth entering the soil, resulting in large soil disturbance, high power consumption and severe vibration of the whole planter, and generating a certain amount of topsoil loss, higher operating cost, lower seeding quality and poor comfort and reliability of the machine.

In view of the above problems existing in 2BMFJ series straw clearing and mulching no-tillage precision planter, Wang Hanyang et al. [5] adopted the orthogonal test method to carry out the parameter combination improvement test of the influence of rigid teeth arrangement, rotational speed and machine forward speed on soil disturbance quantity. Dun Guoqiang et al. [6] conducted theoretical analysis and parameter combination improvement test on the influence of the rotation direction of rigid teeth on the torque characteristics. Chen Haitao et al. [7] adopted the orthogonal test method and applied the dynamic signal acquisition system to carry out the parameter combination improvement test on the influence of the number of rigid teeth, arrangement and rotate speed on equivalent power consumption and vibration intensity. Hou Shouyin et al. [8,9] designed a lateral straw clearing knife and a lateral stubble clearing knife with special edge curve and carried out parameter combination improvement test. The results showed that the soil disturbance amount of the rigid tooth type straw clearing and mulching roller was 80%, the equivalent power consumption was 3 kW and the vibration intensity was 200 m/s². Based on the above analysis, it can be seen that the current research on lateral straw clearing and mulching technology mainly takes rigid tooth type lateral straw clearing roller as the research object, and the value range and combination of influencing factors such as the arrangement mode, number, rotational speed and edge curve of rigid teeth are optimized to reduce soil disturbance, power consumption and vibration.

Based on the above research status, this paper designed an elastic tooth type lateral straw clearing roller to reduce soil disturbance, power consumption and vibration. By analyzing the operation process of the elastic tooth in the aspects of mechanics and kinematics, the mathematical model of the relation between the total deformation angle of the elastic tooth and the position displacement, velocity and acceleration of tooth rod end was established, and the influence law of each parameter on the dynamic characteristics of the tooth rod was clarified. The structure and arrangement of elastic teeth were designed, and the key parameters and value range that affected the operation performance of the elastic tooth type lateral straw clearing roller were determined. Field experiments were carried out by orthogonal test method to obtain the optimal combination of parameters affecting the performance of the elastic tooth type lateral straw clearing roller.

2. Materials and Methods

2.1. Design of the Elastic Tooth Type Lateral Straw Clearing Roller

2.1.1. The Overall Scheme of the Elastic Tooth Type Straw Clearing and Mulching No-Tillage Precision Planter

The overall scheme of the elastic tooth type straw clearing and mulching no-tillage precision planter is shown in Figure 1. The planter was connected with the tractor through a traction frame or a three-point suspension device. The sowing devices, fertilizing openers, a fertilizer box and ground wheels are arranged on the frame and the straw mulching control board is hinged on one side of the frame. The elastic tooth type lateral straw clearing rollers are fixed on the frame in front of the seeding devices in the axial direction parallel to the forward direction of the planter. Through the transmission system, the rotary power provided by the tractor is adjusted to drive the rollers to rotate around the fixed axis at a high speed. The high-speed rotating elastic teeth can clear and throw the straw from the corresponding sowing and fertilizing row to create a straw-free surface for subsequent sowing and fertilizing, which can effectively improve the sowing quality and operation efficiency. At the same time, by adjusting the angle of the straw mulching control board, the thrown straw can cover the adjacent sown area in the entire operation width evenly. In the process of using elastic teeth to lateral dispose straw, because the elastic teeth have self-deformation characteristic, they can always contact with the ground surface, avoiding a series of problems such as overweight design, large soil disturbance, high power consumption and severe mechanical vibration caused by increasing the weight of the planter and the depth of rigid teeth into the soil to ensure the quality of straw clearing.

2.1.2. Structure and Operation Principle of the Elastic Tooth Type Lateral Straw Clearing Roller

The overall structure of the elastic tooth type lateral straw clearing roller is shown in Figure 2a. The elastic teeth are fixed with the pin shafts through the elastic tooth locking bolts, and the pin shafts are fixed with the elastic tooth seats circumferentially welded on the roller through the pin shaft locking screws. The roller is fixedly connected with the drive sprocket, and can be rotatedly assembled on the fixed shaft, which cannot move because of the constraints on the shaft. The fixed shaft is fixed on the frame through the supports at both ends, which improves the strength and stiffness of the U-shaped frame.

The operation principle is shown in Figure 2b. The elastic tooth type lateral straw clearing roller moves in a straight line along the axial direction with the planter and rotates at a high speed around the axis of fixed shaft. The elastic teeth arranged evenly in the circumferential direction carry out straw clearing in turn. When the elastic tooth contacts with the ground, under the combined action of soil resistance, surface friction and machine gravity, the elastic tooth torsion spring produces torsional deformation, and the tooth rod rotates around the axis of the pin shaft in the reverse direction of rotation of the roller. This deformation reduces the absolute velocity of contact between elastic teeth and soil and effectively avoids the impact of rigid teeth entering the soil. The torsion spring generates torsion force and drives the elastic tooth rod to always contact with the ground during operation, and the elastic tooth rod is deformable, which ensures that the straw within the operation width is always located in the plane formed by the elastic tooth and the ground avoiding straw leakage.

2.1.3. Force Analysis of the Elastic Tooth

The elastic tooth deformation characteristics of the elastic tooth type lateral straw clearing roller can not only reduce soil disturbance, power consumption and vibration, but also realize elastic copying according to the ground unflatness, which can effectively avoid the phenomenon of straw leakage due to the change of surface elevation. In other words, the elastic action of the elastic tooth deformation makes the tooth rod always contact with the ground.

The deformation of the elastic tooth includes torsion deformation of the torsion spring and bending deformation of the tooth rod. The torsion deformation amount is mainly determined by the screw pitch diameter, winding number, elastic tooth wire diameter and material properties of the torsion spring, and the bending deformation amount is mainly determined by the length of tooth rod, elastic tooth wire diameter and material properties [10]. The analysis shows that when the deformation amount of the elastic tooth is too large, the lateral force of tooth rod on straw is mainly the friction force of elastic tooth on straw, which is far less than the friction force of ground on straw, and the straw clearing effect is poor. When the deformation amount of the elastic tooth is too small, there will be no contact between the tooth rod and the ground under the condition of large surface unflatness, that is, the deformation amount of the elastic tooth is not enough to compensate the surface unflatness, resulting in straw leakage. The force analysis on the lateral straw clearing process of the elastic tooth is shown in Figure 3, and the force equation of straw can be obtained as follow:

$$\left\{\begin{array}{l}{F}_{\mathrm{N}}\cos \theta +f_1\sin \theta \ge f_2\\ N+f_1\cos \theta -mg-F_{\mathrm{N}}\sin \theta =0\\ \theta ={\theta }_1+{\theta }_2\\ {\theta }_1=\frac{64F_{\mathrm{N}}l}{\mathsf{\pi }E{d}_0{}^4}\left(\mathsf{\pi }z{D}_0+\frac{l}{3}\right)\\ {\theta }_2=\frac{8l^2{F}_{\mathrm{N}}}{45E{d}_0{}^4}\\ f_1={\mu }_1{F}_{\mathrm{N}}\\ f_2={\mu }_{2}N\end{array}\right.$$

(1)

where F_N is the positive pressure of the tooth rod on the straw, N; θ is the total deformation angle of the elastic tooth, rad; f₁ is the friction force of the tooth rod on the straw, N; f₂ is the friction force of the ground on the straw, N; N is the supporting force of the ground on the straw, N; m is the quality of the straw, kg; θ₁ is the torsion deformation angle, rad; θ₂ is the bending deformation angle, rad; l is the length of tooth rod, mm; E is the elastic modulus of the elastic tooth, MPa; d₀ is the elastic tooth wire diameter, mm; z is the winding number of the torsion springs; D₀ is the screw pitch diameter of the torsion spring, mm; μ₁ is the friction coefficient between the tooth rod and the straw; μ₂ is the friction coefficient between the soil and the straw.

The volume and mass of crushed corn straw in spring sowing period are small, so the influence of gravity on the force system can be ignored. According to Equation (1), it can be known that the torsion deformation amount of the torsion spring is much larger than the bending deformation amount of the tooth rod in the operation process, so the bending deformation angle can be ignored in the subsequent design. According to Equation (1), the expression of the total deformation angle of the elastic tooth in the operation process is as follow:

$$\left\{\begin{array}{l}\theta =\frac{64F_{\mathrm{N}}l}{\mathsf{\pi }E{d}_0{}^4}\left(\mathsf{\pi }z{D}_0+\frac{l}{3}\right)\\ \theta \le \arctan \left(\frac{{\mu }_2-{\mu }_1}{1+{\mu }_1{\mu }_2}\right)\end{array}\right.$$

(2)

According to Equation (2), the total deformation angle is related to the length of tooth rod, the winding number of the torsion springs, the screw pitch diameter of the torsion spring, the positive pressure of the tooth rod on the straw, the elastic modulus of the elastic tooth and the elastic tooth wire diameter. The parameters except the positive pressure of the tooth rod on the straw are all quantitative and can be determined according to the actual functional requirements, and the total deformation angle is positively correlated with the positive pressure of the tooth rod on the straw. When the total deformation angle is too large, the horizontal pushing force exerted on the straw is less than the friction force of the ground on the straw, resulting in straw cannot be cleared. According to Equation (2), the maximum allowable design of the total deformation angle is determined by the friction coefficient between the tooth rod and the straw, and the friction coefficient between the soil and the straw. By referring to the correlation study of straw friction coefficient [11], the known data are inserted into Equation (2), and the maximum total deformation angle is no more than 0.33 rad.

2.1.4. Kinematics Analysis of the Elastic Tooth

In the operation process of the elastic tooth type lateral straw clearing roller, the main working component is the tooth rod of the elastic tooth. After contacting with the ground, the tooth rod mainly moves along with the roller and rotates around the pin shaft. In order to clarify the variation rule of related kinematic parameters during the operation process of the tooth rod, and to provide basis for the design of the elastic tooth and the selection of key parameters of the roller, the kinematic analysis is carried out.

In the rotation plane of the roller, the ground plane is defined as the abscissa, the vertical line of the ground passing through the rotation center of the roller is defined as the ordinate, and the intersection point O is defined as the origin of the coordinates. For the convenience of analysis, the structure of the roller and the elastic tooth is simplified, as shown in Figure 4, in which AB rod is the elastic tooth, BC rod is the rotation radius of the roller, point C is the rotation center of the roller and point B is the center of the pin shaft. Through the above force analysis, only the torsion deformation of the elastic tooth is considered, the tooth rod is regarded as rigid body, and the influence of the deformation of the torsion spring on the length of tooth rod is ignored, that is, the elastic tooth rotates only around the pin shaft, and the length of tooth rod remains unchanged. It can be seen from the analysis that there are three main processes from the contact between the tooth rod and the ground to the separation, including the pressurization torsion, the decompression torsion and the ejection. The pressurization torsion process is located on the left side of y axis, and the decompression torsion and ejection process are located on the right side of y axis. Due to the torsion spring pressure, point A at the end of the tooth rod always keeps in contact with the ground, and the displacement equation of point A is established as follow:

$$\left\{\begin{array}{l}x=-l_0\sin \alpha -\sqrt{L^2-{\left(h-l_0\cos \alpha \right)}^2}\\ L=\sqrt{l^2+{\frac{D_0}{4}}^2}\\ \alpha ={\alpha }_0-\omega t\end{array}\right.$$

(3)

where x is the displacement amount of the end of the tooth rod, mm; l₀ is the rotation radius of the roller, mm; h is the clearance of roller center from ground, mm; ω is the angular velocity of roller, rad/s; t₀ is the time when point A first makes contact with the ground, s; t₁ is the time when point A is at the center line of the roller, s; t₂ is the time when the line between point A and the center of the pin shaft is perpendicular to the ground, s; α₀ is the starting angle, rad.

By taking the first and second derivatives of Equation (3), the velocity and acceleration equations of point A at the end of the tooth rod can be obtained as follow:

$$\left\{\begin{array}{c}{v}_{\mathrm{A}}=l_0\omega \left(\cos \alpha -\frac{\sin \alpha }{\sqrt{\frac{L^2}{{\left(h-l_0\cos \alpha \right)}^2}-1}}\right)\hfill \\ a_{\mathrm{A}}=l_0{\omega }^2\sin \alpha +\frac{l_0{\omega }^2\cos \alpha }{\sqrt{\frac{L^2}{{\left(h-l_0\cos \alpha \right)}^2}-1}}+\frac{L^2{l}_0{}^{2}l{\omega }^2{\sin }^2\alpha }{{\left(h-l_0\cos \alpha \right)}^3\sqrt{{\left(\frac{L^2}{{\left(h-l_0\cos \alpha \right)}^2}-1\right)}^3}}\hfill \end{array}\right.$$

(4)

The elastic tooth type lateral straw clearing roller designed in this paper is mainly used in the straw clearing and mulching no-tillage precision planter with 650 mm row spacing cultivation mode. According to the analysis of a related reference [12], based on the limiting condition of straw length with stubble height of 700 mm, in order to prevent straw from winding the roller, the rotary radius of the roller should be greater than 112 mm, and 120 mm is selected in this paper. At the same time, in order to ensure no interference between adjacent rollers and elastic teeth, the design value of the rotary radius of elastic teeth should be less than 430 mm. The larger the rotary radius of elastic teeth is, the larger the clearance between the frame and ground is, and the better the passing ability of the planter in the operating direction. Combined with the structure design of the frame, the rotary radius of elastic teeth is selected as 390 mm. The theoretical deformation amount selected initially of the elastic tooth in the y axis direction is 30 mm, and the clearance of roller center from ground is 360 mm. Since the value of the screw pitch diameter of the torsion spring is relatively small, which can be ignored, the starting angle is determined as 0.39 rad by the rotary radius of elastic teeth and the clearance of roller center from ground. According to Equation (4), when the starting angle is less than π/2, the velocity and acceleration of point A at the end of the tooth rod are both greater than 0, which means the end of the tooth rod always accelerates. This is mainly because when the elastic tooth contacts the ground, the torsion deformation of the torsion spring converts part of the kinetic energy into elastic potential energy and reserves it, resulting in the reduction of the initial kinetic energy and small initial linear velocity of the elastic tooth. With the release of the elastic potential energy, the kinetic energy increases and the linear velocity of the elastic tooth increases. The movement law of the contact velocity between the elastic tooth and the ground increases gradually from small to large, which can effectively reduce the violent vibration of the planter caused by high-speed impact when the elastic tooth contact with the ground, and increase the horizontal conveying velocity of straw, which is beneficial to improve the operating efficiency.

The included angle between the tooth rod and the ground surface has an important influence on straw conveying, and the larger the angle is, the better the conveying effect of the straw. When the rotation radius of the roller and the clearance of roller center from ground are constant, the increase of the included angle not only affects the length of tooth rod, but also reduces the deformation amount of the elastic tooth in the vertical direction of the ground. There is no pretightening force before the elastic tooth contacts the ground, BC rod is parallel to AB rod, that is, the initial torsional deformation angle is zero, so the mathematical equation of the included angle between the tooth rod and the ground surface can be expressed as follow:

$$\beta =\arcsin \left(\frac{2h-2l_0\cos \left({\alpha }_0-6\omega t\right)}{\sqrt{4l^2+D^2{}_0}}-\arctan \frac{D_0}{2l}\right)$$

(5)

where β is the included angle between the tooth rod and the ground surface, rad.

According to Equation (5), the included angle between the tooth rod and the ground surface decreases first and then increases, and reaches the minimum when BC rod is perpendicular to the ground. The minimum included angle between the tooth rod and the ground surface should be greater than the friction angle between the tooth rod and straw.

2.1.5. Design of the Elastic Tooth

The elastic tooth is the key operating component of the lateral straw clearing roller, and its operating performance directly affects the quality of straw clearing on the ground, which is mainly influenced by the structure and mechanical parameters of the elastic tooth [13,14,15,16]. Through kinematic analysis of the elastic tooth, the total deformation angle of the elastic tooth can be obtained as follow:

$$\theta =\frac{\mathsf{\pi }}{2}+\left|\alpha \right|-\arcsin \left(\frac{2h-2l_0\cos \alpha }{\sqrt{4l^2+D^2{}_0}}-\arctan \frac{D_0}{2l}\right)$$

(6)

According to Equation (6), the total deformation angle decreases first, then increases and then decreases with the rotation of the roller, that is, the total deformation angle has a maximum value. According to the analysis of Equation (6), when point A at the end of the tooth rod is located at the origin of coordinates, the total deformation angle reaches the maximum value. Combining with Equation (3), the angular displacement of BC rod can be expressed as follow:

$${\alpha }_1=\arccos \left(\frac{h^2+l_0{}^2-L^2}{2h{l}_0}\right)$$

(7)

where α₁ is the included angle between the BC rod and y axis when point A is located at the origin of coordinates, rad.

In order to ensure the normal operation of the elastic tooth, the design value of the total torsional deformation should not be greater than the theoretical value determined by force analysis. The allowable total deformation angle of this design is 0.33 rad. By combining Equations (2), (5) and (7), the following equations can be obtained.

$$\left\{\begin{array}{c}\left[\theta \right]=\frac{64F_{\mathrm{N}}l}{\mathsf{\pi }E{d}_0{}^4}\left(\mathsf{\pi }z{D}_0+\frac{l}{3}\right)\hfill \\ \left[\theta \right]=\frac{\mathsf{\pi }}{2}+\arccos \left(\frac{h^2+l_0{}^2-L^2}{2h{l}_0}\right)-\arcsin \left(\frac{h^2-l_0{}^2+L^2}{h\sqrt{4l^2+D^2{}_0}}-\arctan \frac{D_0}{2l}\right)\hfill \end{array}\right.$$

(8)

where [θ] is the allowable total deformation angle, rad.

In the operating process of the elastic tooth type lateral straw clearing roller, the elastic tooth is subject to the action of periodic variable loads and is prone to fatigue failure. The design of the elastic tooth fatigue life is more than 107 times. According to the design requirement of fatigue life [10], quenching-tempering spring steel wire 55CrSi material is selected with elastic modulus 206 × 103 MPa and allowable stress 1750 MPa. The wire diameter is initially selected as 8 mm. The screw pitch diameter of the torsion spring is designed as 30 mm according to the pin shaft size. By substituting the known conditions into Equation (8), the length of tooth rod is 270 mm. The axis of the elastic tooth type lateral straw clearing roller is arranged in parallel with the forward direction of the planter, so that the longitudinal stability of the planter is reduced if the length of the roller is too large, and the comprehensive utilization rate of supporting power is low. The axial length of the elastic tooth torsional spring is one of the key parameters to determine the length of roller. Under the condition of satisfying the function prerequisite, the less the winding number of the torsion springs, the smaller the axial length. In order to improve the quality of corn straw clearing, the design of elastic teeth is a horizontal double twist structure. According to the average length of corn straw harvested by machines is 100 mm, the spacing of two tooth rods is designed to be 70 mm, and the fixed position of M10 bolt is reserved in the middle of the torsion spring. The winding number of the torsion springs is designed to be 3. According to Equation (8), the positive pressure of the tooth rod on the straw is 136 N. The selection of the elastic tooth wire diameter can be checked by the following equation:

$$d_0\ge \sqrt[3]{\frac{10.2K_{\mathrm{b}}{F}_{\mathrm{N}}l}{\left[\sigma \right]}}$$

(9)

where K_b is the curvature coefficient of bending stress; [σ] is the allowable stress, MPa.

The curvature coefficient of bending stress is set to 1, and the known parameters are put into Equation (9) to obtain that the wire diameter should be greater than or equal to 6.1 mm, and the wire diameter is reasonably designed.

2.1.6. Arrangement of Elastic Teeth

The elastic tooth type lateral straw clearing roller mainly realizes the straw clearing on the corresponding sowing and fertilizing row and prevents the straw blocking the soil touching parts. As shown in Figure 4, the straw clearing width of the elastic tooth consists of two parts: the distance from point A to y axis when the tooth rod end contacts the ground surface, and the distance from point A to y axis when the tooth rod is vertical to the ground surface. The theoretical straw clearing width of the elastic tooth can be obtained as 258 mm by geometric relations. According to the actual situation, the width of the soil touching component of the soybean double row opener is large, and the maximum transverse distance of dynamic soil touching is 200 mm [17], which is smaller than the theoretical straw clearing width and meets the working requirements.

The operation width of 2BMFJ-2 straw clearing and mulching no-tillage precision planter is 1300 mm, and the shaft spacing of two elastic tooth type lateral straw clearing rollers is 650 mm. The calculation formula of disturbed straw amount per unit time is as follows:

$$\left\{\begin{array}{l}{M}_1=\frac{K_1{v}_{\mathrm{m}}W{m}_1}{500}\\ K_1=\frac{M_1}{M_0}\end{array}\right.$$

(10)

where M₁ is the disturbed straw amount per unit time, kg/s; K₁ is sraw joint coefficient; v_m is the forward speed, m/s; W is the straw clearing width, mm; m₁ is the straw mulching amount per unit area, kg/m²; M₀ is the straw quantity in the straw clearing width, kg/s.

Most straw disturbed by the elastic teeth breaks away from the operation width of the planter by being thrown laterally by the elastic teeth, and the straw discharge amount per unit time can be obtained as follow:

$$M_2=\frac{K_{2}R\omega l_2{m}_1}{1\times {10}^6}$$

(11)

where M₂ is the straw discharge amount per unit time, kg/s; K₂ is coefficient of moving speed (K₂ < 1); R is the rotary radius of the elastic tooth, mm; l₂ is the axial operation length of the lateral straw clearing roller, mm.

In order to ensure that the straw in the straw clearing width can be discharged smoothly in the operation process, and to avoid the blockage of the soil touching parts caused by the accumulation of straw feeding amount greater than the discharge amount, the following equation should be met:

$$\rho =\frac{M_1}{M_2}=\frac{2000K_1{v}_{\mathrm{m}}W}{K_{2}R\omega l_2}\le 1$$

(12)

The straw joint coefficient is related to many factors such as straw quantity, moisture content and form, and the maximum value of straw joint coefficient is 1.6 according to experimental studies. Due to the elastic deformation after the elastic tooth contact the ground surface, the actual rotation radius becomes smaller, and the end of the tooth rod moves unevenly. The moving velocity of straw is less than that under the condition of rigid teeth, and the coefficient of moving speed is selected as 0.6. The covering size of straw after throwing should not be smaller than the operation width which is 1.3 m, so the minimum angular velocity of the roller can be calculated as 52.5 rad/s. The maximum forward speed of the planter is designed as 2 m/s. The minimum axial operation length of the lateral straw clearing roller is 136 mm by substituting the known conditions into Equation (12). The axial operation length of the lateral straw clearing roller affects the longitudinal stability of the planter. According to the spacing of two tooth rods is 70 mm, in order to ensure the same axial spacing of tooth rods, the axial operation length of the lateral straw clearing roller is designed as 140 mm.

In order to reduce the impact vibration caused by the contact between the elastic teeth and the ground, it is necessary to ensure that the elastic teeth in different rotation planes contact the ground step by step, and no more than two elastic teeth in the same rotation plane contact with the ground at the same time. The relationship between the working angle of the roller and the number of elastic teeth can be obtained as follow:

$$\frac{\mathsf{\pi }}{z_1{z}_2}\le {\alpha }_0\le \frac{2\mathsf{\pi }}{z_1{z}_2}$$

(13)

where z₁ is the circumferential number of elastic teeth in single row; z₂ is the axial row number of elastic teeth.

According to the axial length of the lateral straw clearing roller, the axial row number of elastic teeth is 2. By substituting the known conditions into Equation (13), the circumferential number of elastic teeth in single row is 4–8.

2.2. Parameter Combination Improvement Test

2.2.1. Test Condition

The test was carried out in Xiangyang Experimental Base of Northeast Agricultural University, Harbin, Heilongjiang Province, China from 1 to 10 October 2021. The test area was the original corn stubble field after machine harvesting, the previous corn variety was Ruifuer 1 which adopted 650 mm ridge planting pattern, and the planting density was 85,000 plants/ha. The average soil hardness was 20.3 kg/cm² and water content was 20.7%. The average straw mulching amount was 1.28 kg/m², stubble height was 273 mm and crushed straw length was 90 mm.

2.2.2. Instrument and Equipment

The instruments and equipment used in the test included a 324 type tractor (Ningbo Benye Tractor Manufacturing Co., Ltd., Ningbo, China), a 2BMFJ-2 straw clearing and mulching no-tillage precision planter (Northeast Agricultural University, Harbin, China), a JM5937A dynamic signal testing system (Yangzhou Jingming Technology Co., Ltd., Yangzhou, China), a JNNT-0 strain type torque sensor (Bengbu Sensor System Engineering Co., Ltd., Bengbu, China), a HK9142 acceleration sensor (Qinhuangdao Hengke Technology Co., Ltd., Qinhuangdao, China), a PV6.08 penetration resistance meter (Royal Eijkelkamp Company, Giesbeek, The Netherlands), a DG-101-1S electric thermostatic drying oven (Shaoxing Supo Instrument Co., Ltd., Shaoxing, China) and a HZ-150 electronic scale (Ruian Haozhan Hengqi Co. Ltd., Ruian, China). The connection of instruments and equipment is shown in Figure 5a.

2.2.3. Test Scheme

According to the above theoretical analyses, the main parameters and their theoretical values affecting the performance of the elastic tooth type lateral straw clearing roller were determined. This paper adopted four factors and three levels orthogonal test method, and used L₂₇(3¹³) orthogonal table to design the test. The length of tooth rod, the clearance of roller center from ground, the circumferential number of elastic teeth and the angular velocity of roller were taken as test factors, and straw clearing rate, power consumption and vibration intensity were taken as evaluation indexes. Each group of test treatment was repeated for 3 times, and a total of 27 groups of tests were carried out. Design-Expert 6.0.10 software was used to process and analyze the data of the test results [18]. The level of test factors is shown in

Table 1. Test factors and level.

Level	Factors
	The Length of Tooth Rod l/mm	The Clearance of Roller Center from Ground h/mm	The Circumferential Number of Elastic Teeth z1	The Angular Velocity of Roller ω/(rad·s−1)
1	240	340	4	42.0
2	270	360	6	52.5
3	300	380	8	63.0

, and the test scheme is shown in

Table 2. Test scheme and results.

Test No.	l/mm	h/mm	z1	ω/(rad·s−1)	Straw Clearing Rate/%	Power Consumption/kW	Vibration Intensity/(m·s−2)
1	240	340	6	42	71	1.21	60.5
2	240	340	7	52	76	1.52	76.0
3	240	340	8	62	81	1.78	89.0
4	240	360	6	52	70	1.31	65.5
5	240	360	7	62	78	1.72	86.0
6	240	360	8	42	72	1.31	65.5
7	240	380	6	62	68	1.52	76.0
8	240	380	7	42	60	1.18	59.0
9	240	380	8	52	68	1.53	76.5
10	270	340	6	52	71	1.32	66.0
11	270	340	7	62	78	1.81	90.5
12	270	340	8	42	73	1.42	71.0
13	270	360	6	62	94	1.70	85.0
14	270	360	7	42	84	1.43	71.5
15	270	360	8	52	93	1.67	83.5
16	270	380	6	42	72	1.21	60.5
17	270	380	7	52	81	1.52	76.0
18	270	380	8	62	87	1.79	89.5
19	300	340	6	62	73	1.82	91.0
20	300	340	7	42	67	1.52	76.0
21	300	340	8	52	70	1.91	95.5
22	300	360	6	42	64	1.43	71.5
23	300	360	7	52	74	1.71	85.5
24	300	360	8	62	78	1.97	98.5
25	300	380	6	52	91	1.43	71.5
26	300	380	7	62	93	1.63	81.5
27	300	380	8	42	84	1.47	73.5

.

The measurement methods of evaluation indexes are as follows:

1. Straw clearing rate.

Straw clearing rate refers to the quality ratio of corn straw mulching on the ground after straw clearing operation and before straw clearing operation of the elastic tooth type lateral straw clearing roller in the operation width [19]. Five measuring points were selected randomly on the straw clearing row in the forward direction of the planter, and each measuring point was 200 mm × 200 mm in length and width. The corn straw quality of measuring points before and after the operation was weighed, and the straw clearing rate can be calculated as follow:

$$J=\frac{W_{\mathrm{q}}-W_{\mathrm{h}}}{W_{\mathrm{q}}}\times 100\%$$

(14)

where J is the straw clearing rate, %; W_h is the corn straw quality after operation of each measuring point, kg; W_q is the corn straw quality after operation of each measuring point, kg.

2. Power consumption.

The torque sensor was installed between the power output shaft of the tractor and the input shaft of the planter. The average torque of the power output shaft of each test treatment group was recorded through the data acquisition equipment [20,21,22,23], and the power consumption can be calculated as follow:

$$P=\frac{Tn}{9550}$$

(15)

where T is the average torque of the power output shaft, N·m; n is the average rotation speed of the power output shaft, rpm.

3. Vibration intensity.

As shown in Figure 5, the acceleration sensor was installed at the connection position between the planter frame and the support of the lateral straw clearing roller. The vertical acceleration of the planter in the operation process can be measured to characterize the vibration intensity, and the average value in the testing process was taken as the measurement result [24,25,26].

3. Results and Discussion

The test process and measurement process of relevant data are shown in Figure 5. The calculation results of the test measurement data are shown in Table 2, and the variance analysis of the test results is shown in

Table 3. Variance analysis.

Evaluation Indexes	Source	Sum of Squares	df	Mean Square	F	p	Significance
Straw clearing rate	Model	2156.88	12	179.74	47.71	<0.0001
	l	442.29	2	221.14	58.70	<0.0001	**
	h	153.85	2	76.92	20.41	<0.0001	**
	z1	56.96	2	28.48	7.56	0.0059	**
	ω	384.96	2	192.48	51.09	<0.0001	**
	l × h	1118.81	4	279.70	74.24	<0.0001	**
	Error	52.74	14	3.76
	Cor Total	2209.62	26
Power consumption	Model	1.16	8	0.14	26.70	<0.0001
	l	0.18	2	0.09	16.80	<0.0001	**
	h	0.07	2	0.03	6.81	0.0062	**
	z1	0.20	2	0.10	18.54	<0.0001	**
	ω	0.70	2	0.35	64.65	<0.0001	**
	Error	0.09	18	0.01
	Cor Total	1.26	26
Vibration intensity	Model	2765.77	6	460.96	20.60	<0.0001
	l	445.40	2	222.70	9.95	0.0010	**
	z1	499.85	2	249.92	11.17	0.0006	**
	ω	1820.51	2	910.25	40.69	<0.0001	**
	Error	447.40	20	22.37
	Cor Total	3213.18	26

Note: ** means extremely significant (p < 0.01).

.

According to Table 3, as for the straw clearing rate, all the test factors and the interaction between the length of tooth rod and the clearance of roller center from ground have extremely significant effects on the test results, and the influence order from the largest to the smallest is the length of tooth rod, the angular velocity of roller, the clearance of roller center from ground and the circumferential number of elastic teeth. As for the power consumption, all the test factors have extremely significant effects on the test results, and the influence order from the largest to the smallest is the length of tooth rod, the angular velocity of roller, the circumferential number of elastic teeth and the clearance of roller center from ground. As for the vibration intensity, the length of tooth rod, the circumferential number of elastic teeth and the angular velocity of roller have extremely significant effects on the test results, while the clearance of roller center from ground has no significant effect on the test results, and the influence order from the largest to the smallest is the angular velocity of roller, the angular velocity of roller, the length of tooth rod and the clearance of roller center from ground.

3.1. Influence Analysis of Various Test Factors on Straw Clearing Rate

Figure 6a shows that when the circumferential number of elastic teeth and the angular velocity of roller are at the center level, the interaction between the length of tooth rod and the clearance of roller center from ground has an impact on the straw clearing rate. When the clearance of roller center from ground is 340 mm, the straw clearing rate decreases with the increase of the length of tooth rod, which is mainly because the included angle between the tooth rod and the ground surface decreases with the decrease of the clearance of roller center from ground, resulting in the decrease of the resultant force of the tooth rod on straw in horizontal direction and the decrease of the straw clearing rate. When the clearance of roller center from ground is 360 mm, the straw clearing rate increases first and then decreases with the increase of the length of tooth rod, mainly because when the length of tooth rod is 240 mm, the torsion variable of the elastic tooth is small when the elastic teeth contact the ground, and the phenomenon of straw leakage is easy to occur. When the length of tooth rod is 300 mm, the torsion variable is large, the included angle between the tooth rod and the ground surface decreases, and the straw clearing effect decreases. When the clearance of roller center from ground is 380 mm, the straw clearing rate increases gradually with the increase of the length of tooth rod, mainly because when the length of tooth rod is less than 300 mm, the torsion variable of the elastic tooth cannot completely meet the requirements of the copying amount required by surface unflatness, and the phenomenon of straw leakage is easy to occur. When the clearance of roller center from ground and the angular velocity of roller are at the center level, the straw clearing rate increases with the increase of the circumferential number of elastic teeth, and when the clearance of roller center from ground and the circumferential number of elastic teeth are at the center level, the straw clearing rate increases with the increase of the angular velocity of roller. This is mainly because the increase of the circumferential number of elastic teeth and the angular velocity of roller reduces the pitch of straw clearing by elastic teeth on the ground and effectively improves the straw clearing rate.

3.2. Influence Analysis of Various Test Factors on Power Consumption

According to Figure 6b, when the circumferential number of elastic teeth and the angular velocity of roller are at the center level, the power consumption increases with the increase of the length of tooth rod, which is mainly because the torsion variable of the spring tooth increases with the increase of the length of tooth rod, leading to the increase of the friction force between elastic teeth and ground and the increase of power consumption. When the clearance of roller center from ground and the angular velocity of roller are at the center level, the power consumption increases with the increase of the circumferential number of elastic teeth, and when the clearance of roller center from ground and the circumferential number of elastic teeth are at the center level, the power consumption increases with the increase of the angular velocity of roller. This is mainly because the increase of the circumferential number of elastic teeth and the angular velocity of roller improves the number of straw clearing per unit time of elastic teeth and improves the power consumption.

3.3. Influence Analysis of Various Test Factors on Vibration Intensity

According to Figure 6c, the clearance of roller center from ground has no significant effect on the vibration intensity. When the circumferential number of elastic teeth and the angular velocity of roller are at the center level, the vibration intensity increases with the increase of the length of tooth rod, which is mainly because the length of the tooth bar increases, leading to the increase of the vibration of the elastic tooth during the recovery deformation process of leaving the ground, and the increase of vibration intensity of the whole planter. When the clearance of roller center from ground and the angular velocity of roller are at the center level, the vibration intensity increases with the increase of the circumferential number of elastic teeth, and when the clearance of roller center from ground and the circumferential number of elastic teeth are at the center level, the vibration intensity increases with the increase of the angular velocity of roller. This is mainly because the increase of the circumferential number of elastic teeth and the angular velocity of roller improves the number of the alternating contact between elastic teeth and ground per unit time and improves the vibration intensity.

3.4. Improvements in Parameter Combination

Based on the principle of improving the straw clearing rate of the elastic tooth type lateral straw clearing roller, and reducing power consumption and vibration intensity, under the forward speed of 7.2 km/h, in order to realize the straw clearing rate greater than 90%, the power consumption less than 1.7 kW and the vibration intensity less than 85 m/s², Design-expert 6.0.10 software was used for optimization, and the optimization combination results of the structure and working parameters of the elastic tooth type lateral straw clearing roller were shown in

Table 4. Optimization combination and verification results.

Improved Parameter Combination				Straw Clearing Rate/%	Power Consumption/kW	Vibration Intensity/(m·s−2)
The Length of Tooth Rod l/mm	The Clearance of Roller Center from Ground h/mm	The Circumferential Number of Elastic Teeth z1	The Angular Velocity of Roller ω/(rad·s−1)
270	360	8	52	92	1.65	83
				93	1.62	82
				92	1.67	85

. The field validation test was conducted according to the improved parameter combination, and the tests were repeated for three times, with the results shown in Table 4. Each evaluation index value conformed to the optimization principle and practical operation requirements, which proved that the optimization results were credible.

In order to verify the difference of evaluation indexes between elastic tooth type and rigid tooth type lateral straw clearing rollers in the same operating environment, the two rollers were respectively assembled on 2BMFJ-2 type straw clearing and mulching no-tillage precision planter for comparative test. The lateral straw clearing rollers used in the comparative test are shown in Figure 7.

In the test process, when the straw clearing rate of the rigid tooth type lateral straw clearing roller was more than 90%, the amount of soil moving was large, the mixture of soil and straw was serious, and the dust phenomenon was obvious. The dust phenomenon of the elastic tooth type lateral straw clearing roller was not obvious, indicating that the amount of soil disturbance was small. Under the same operating conditions, the straw clearing rate, power consumption and vibration intensity of the elastic tooth type lateral straw clearing roller and the rigid tooth type lateral straw clearing roller were 93%, 1.65 kW, 84 m/s² and 90%, 4.5 kW, 148 m/s², respectively. Compared with rigid tooth type lateral straw clearing roller, the power consumption and vibration intensity of the elastic tooth type lateral straw clearing roller were reduced by 63.3% and 43.2%, respectively, which showed that the elastic tooth structure could reduce the consumption and vibration significantly in straw clearing process.

4. Conclusions

Aiming at the problems of large soil disturbance, high power consumption and strong vibration during the operation of the 2BMFJ series straw clearing and mulching no-tillage precision planter with rigid teeth, an elastic tooth type lateral straw clearing roller was designed, and the key parameters and values affecting the operation performance of the device were determined. The parameter combination improvement test was implemented with the length of tooth rod, the clearance of roller center from ground, the circumferential number of elastic teeth and the angular velocity of roller as test factors, and straw clearing rate, power consumption and vibration intensity as performance evaluation indexes, and the improved parameter combination was obtained. At the same time, the operation performance comparison test between the elastic tooth type and rigid tooth type lateral straw clearing rollers under the improved parameter combination was conducted.

(1)

As for the straw clearing rate, all the test factors and the interaction between the length of tooth rod and the clearance of roller center from ground have extremely significant effects on the test results, and the influence order from the largest to the smallest is the length of tooth rod, the angular velocity of roller, the clearance of roller center from ground, and the circumferential number of elastic teeth. As for the power consumption, all the test factors have extremely significant effects on the test results, and the influence order from the largest to the smallest is the length of tooth rod, the angular velocity of roller, the circumferential number of elastic teeth and the clearance of roller center from ground. As for the vibration intensity, the length of tooth rod, the circumferential number of elastic teeth and the angular velocity of roller have extremely significant effects on the test results, while the clearance of roller center from ground has no significant effect on the test results, and the influence order from the largest to the smallest is the angular velocity of roller, the angular velocity of roller, the length of tooth rod and the clearance of roller center from ground.

(2)

Under the condition of 7.2 km/h forward speed, when the length of tooth rod was 270 mm, the clearance of roller center from ground was 360 mm, the circumferential number of elastic teeth was 8, and the angular velocity of roller was 52 rad/s, the straw clearing rate was more than 90%, the power consumption was less than 1.7 kW, and the vibration intensity was less than 85 m/s². Compared with rigid tooth type lateral straw clearing roller, there was no significant difference in straw clearing rate of the elastic tooth type lateral straw clearing roller, but the power consumption and vibration intensity had significant differences and were reduced by 63.3% and 43.2%, respectively.

The results provide key technical support for the high quality, low consumption and reliable operation of 2BMFJ series straw clearing and mulching no-tillage precision planter, and provide a reference scheme for reducing consumption and vibration in the process of straw mulching no-tillage seeding, which will produce significant economic, social and ecological benefits in agricultural production. This study was carried out under the specific conditions of soil moisture content, straw mulching amount and straw crushing length. For other environments and working conditions, whether the improved parameter combination met the working requirements needed further confirmation. At the same time, this paper only carried out an experimental study of design and parameter combination on the elastic tooth type lateral straw clearing roller from the aspect of practical application, and did not deeply explore the law of straw moving and the mechanism of the reduction of consumption and vibration of the elastic tooth, which would be the focus of future research.