Structural Design and Testing of a Corn Header for Soybean–Corn Intercropping

Abstract

In response to the issues that existing corn headers are not only unsuitable for harvesting under the strip intercropping mode of soybeans and corn but also have the problems of being heavy and causing high harvest losses, a new type of header has been designed. This new header is lighter, reduces harvest losses, and is specifically adapted for use in the strip intercropping mode of soybeans and corn. By analyzing the corn stalks and the growth conditions of the corn, efforts were made to reduce the loss rate of kernels during harvesting, leading to a structural design of the header frame tailored for the strip intercropping mode. Following this, finite element analysis was employed to achieve a lightweight design of the header. The results show that the optimized header is 28.4 kg lighter than the original. The optimal working parameter combination for the combine harvester includes a forward speed of 0.94 m/s, a stalk roll rotational speed of 566.5 r/min, and a kernel moisture content of 25%, under which conditions the grain loss rate of the corn header is 0.32% and the ear loss rate is 1.1%. The development of this specialized corn header is conducive to enhancing both the quality and efficiency of mechanized harvesting in the strip intercropping mode of soybeans and corn.

1. Introduction

The strip intercropping system for soybean and maize is grounded in the principles of efficient light energy utilization and field configuration technology. This approach addresses the challenge of achieving high yields from both tall and short crops simultaneously. It enables farmers to maintain or even increase maize yields while significantly boosting soybean production within a single growing season, achieving a land equivalent ratio as high as 1.42 [1,2,3]. By 2022, the planting area utilizing this method in China had reached approximately one million hectares. However, the unique characteristics of this planting pattern pose challenges for traditional maize harvesters, often resulting in suboptimal harvest quality [4,5].

Ear picking is a crucial component of corn harvesting. Virtual simulation experiments have demonstrated that optimal mechanical harvesting quality is achieved when the ear-picking roller operates at a moderate speed and the edge angle of the picking plate is maintained between 13° and 15° [6]. Studies on the mechanical characteristics of corn ear picking indicate that factors influencing kernel damage include the speed of the ear-picking roller, the threshing gap, and the feeding rate [7]. To address the specific requirements of intercropping systems, Shihezi University has developed an upland gap corn seed harvester capable of simultaneously harvesting corn in two belts and four rows, effectively navigating through soybean rows and doubling the harvesting efficiency [8]. Furthermore, the Nanjing Institute of Agricultural Mechanization has introduced an integrated soybean and maize harvester designed to simultaneously harvest maize cobs and soybean grains [9]. However, the row spacing for the corn header on this harvester ranges from 600 to 800 mm, which can result in misalignment during the corn harvesting process, leading to increased losses during mechanized harvesting [10].

Due to new harvesting requirements and new cultivation methods, existing corn headers do not meet the new harvesting needs. Corn planting requires different row spacings in different regions and different planting techniques. Inner Mongolia Agricultural University has designed a corn header for wide and narrow rows with a grain loss rate of 0.14% [11]. To reduce losses during ear picking, Jilin University has designed a biomimetic corn ear picker that mimics the process of humans picking corn ears, using a reverse biomimetic picking head [12].

To further enhance the quality of corn harvesting in soybean–corn strip intercropping systems, this paper presents the design of a specialized two-row corn header. Tailored to fit the specific planting characteristics of corn and the structural requirements of the Jinxing 4LZ-1.6Z combine harvester, this design integrates an optimized dimensional approach. Additionally, field trials were carried out to determine the optimal combination of operational parameters, ensuring efficient and effective harvesting performance.

2. Design of a Specialized Two-Row Corn Header

2.1. Design Method

To prevent losses at the corn header due to misalignment during the corn harvesting process, a schematic diagram of the misalignment phenomenon is shown in Figure 1.

In strip intercropping mode, the corn planting row spacing is 400 mm, the plant spacing is 100–170 mm, and the distance between corn and soybean strips is 600–700 mm [13], as shown in Figure 2.

Based on the characteristics of corn planting in the strip intercropping mode with soybeans and the attachment structure of the Jinxing 4LZ-1.6Z combine harvester, a design calculation for the corn header was conducted, and JinXing 4LZ-1.6Z parameters are shown in

Table 1. Relevant parameters of Jinxing 4LZ-1.6Z.

Item	Parameter
Boundary dimension/(mm)	5100 × 2035 × 2080
Engine power/(kw)	44.2
Feed quantity/(kg)	2.2
Number of harvested rows	2
Overall machine quality/(kg)	2160
Minimum ground clearance/(mm)	280

.

2.2. Ear-Picking Gearbox Design

The ear-picking gearbox, as an essential component of the corn header’s ear-picking device, fundamentally works by distributing the input power to a set of counter-rotating grain sprockets and a set of counter-rotating stalk rolling power couplings [14]. The row spacing of the corn header is the distance between the central planes of two adjacent ear-picking gearboxes. When the installation positions of two gearboxes are in contact, the row spacing of the corn header is minimized. However, due to the large size of existing ear-picking gearbox products, even when two gearboxes are in contact, the row spacing of the corn header still exceeds 400 mm, which does not meet the requirements for row harvesting. To address this issue, the original gearbox transmission is simplified, and the two gearboxes of the two-row corn header are combined into one large gearbox to achieve the design goal of a 400 mm row spacing, as shown in Figure 3.

2.3. Calculation of Parameters Related to the Ear-Picking Device

The ear-picking device, as the core component of the corn header, consists of stalk rolls, ear-picking plates, and grain chains. Its structural and operational parameters determine the working quality of the corn header. An illustration of the ear-picking process is shown in Figure 4.

2.3.1. Design of Stalk Roll Length

The length of the stalk rolls is related to the plant height and the inclination angle of the header [15]. The total length L of the stalk roll is given by Equation (1).

$$L=(h_b-h_s)\sin \theta$$

(1)

where h_b is the height of the corn stalk (mm); h_s is the distance from the corn header to the ground (mm); and θ is the inclination angle of the corn header (°).

For this paper, the selected range for plant height h_b is 1800 mm–2600 mm [16], the height of the corn header from the ground h_s is set at 600 mm, and the inclination angle θ is set at 15°. By substituting these specific values into Equation (1), the length L of the stalk rolls is determined to range from 310.6 mm to 517.6 mm. To satisfy the harvesting of most corn plants, the length of the stalk rolls is set at 520 mm.

2.3.2. Determination of Working Parameters for the Ear-Picking Device

During the ear-picking operation of the corn header, the posture of the stalks is related to the forward speed of the harvester, the linear speed of the stalk rolls, and the linear speed of the grain chains. The ratio of the grain chain’s linear speed v_b to the stalk roll’s linear speed v_l being too high or too low can affect the quality of the corn header’s operation [17,18,19,20]. In an ideal state, during the stalk feeding phase, the horizontal component of the grain chain’s linear speed v_b should be equal in magnitude but opposite in direction to the harvester’s forward speed v₀; during the stalk pulling phase, the horizontal component of the stalk roll’s linear speed v_l should be equal in magnitude but opposite in direction to the harvester’s forward speed v₀. At this time, the corn stalks remain in a vertical position, ensuring a high-quality ear-picking operation.

However, in reality, due to factors such as the growth state of field plants, varieties, and stalk moisture content, it is inevitable that plants may lean forward or fall backward during the ear-picking operation. To address this, a correction coefficient λ is introduced [21]. To ensure normal stalk pulling during the ear-picking operation of the corn header, the following equations should be satisfied:

$$\left\{\begin{array}{l}{v}_0=\lambda v_b\cos \theta \\ v_0=v_l\sin \theta \\ v_l=\pi nD\end{array}\right.$$

(2)

where v₀ is the forward speed of the combine harvester, m/s; v_b is the linear speed of the grain chains, m/s; v_l is the linear speed of the stalk rolls, m/s; n is the rotational speed of the stalk rolls, r/min; and D is the diameter of the stalk rolls, mm.

For the Jinxing 4LZ-1.6Z combine harvester with a maximum travel speed of 1.2 m/s, to ensure harvesting efficiency, the equipment’s travel speed range v₀ is set between 0.8 m/s and 1.2 m/s. The correction coefficient λ is chosen as 1.05, and the diameter of the stalk rolls is 118 mm. Substituting these values into Equation (2) yields a grain chain linear speed range of 0.79–1.18 m/s and a stalk roll linear speed range of 3.09–4.64 m/s, corresponding to stalk roll rotational speeds n of 500 r/min–751.4 r/min.

2.4. Corn Header Frame Design

The corn header frame is a vital component of the header and is responsible for supporting key elements such as the ear-picking gearbox, stalk rolls, and the auger, as well as connecting to the feeder house [22], as illustrated in Figure 5. The connection between the corn header and the feeder house is established by fitting the upper crossbeam of the header frame into the connecting groove at the end of the feeder house, while the lower crossbeam of the corn header frame is securely bolted to the feeder house.

During the mechanical harvesting of corn in soybean–corn strip intercropping systems, the harvester navigates between two soybean strips. Given that the width between these strips is only 1.8 m, the lateral movement space for the harvester is quite limited, as depicted in Figure 6. To avoid damaging the soybean strips, the harvester typically follows the central axis of the corn strip, ensuring that the machine’s center plane aligns with the center plane of the corn strip.

Moreover, to guarantee precise row harvesting, the center plane of the ear-picking device on the header must also align with the center plane of the corn strip. Based on this analysis, it is clear that the machine can harvest corn rows without harming the soybean strips only when the center planes of the corn strip, the machine, and the ear-picking device are perfectly aligned.

The side of the ear-picking device section of the corn header that is away from the feeder house coincides with the side of the header. When the center plane of the ear-picking device section aligns with the center plane of the combine harvester, the lateral width s of the corn header frame is given by the following:

$$s=w_1+w_2+2d$$

(3)

where w₁ is the distance from the side of the ear-picking device farthest from the feeder house to the outer side of the feeder house, mm; w₂ is the distance required for the installation of the transmission device, mm; and d is the thickness of the corn header’s side plate, mm.

Given that w₁ is 1105 mm, w₂ is 175 mm, and d is 3 mm, substituting these values into Equation (3) yields a lateral width s of the header frame of 1286 mm.

3. Optimization Design of the Corn Header Frame Structure

The corn header consists of components such as the ear-collecting device, screw auger, divider, and stalk cutter. To effectively harvest corn, many commercial corn headers often use thicker materials to ensure structural reliability. However, using excessively thick materials increases the weight of the combine harvester, which poses a risk of the harvester tilting forward during field operations. In the initial design process of the corn header discussed in this paper, the contours of existing products were referenced, hence the need for lightweight optimization. A lighter header can reduce mechanical vibration and impact, improve operational stability and precision, and further decrease the harvest loss rate.

The corn header frame is constructed from three main crossbeams, three auxiliary longitudinal beams, and two plates, totaling eight welded components. The overall design dimensions of the corn header frame are 673 × 1286 × 653 mm. The component material used has a material density of ρ = 7850 kg/m³, a Poisson’s ratio of 0.33, an elastic modulus of E = 2.1 × 10¹¹ Pa, a yield strength of 235 MPa, and a tensile strength of 500 MPa [23].

3.1. Static Analysis of the Corn Header Frame

3.1.1. Geometric Model Processing

Before performing finite element analysis on the corn header frame, the following preparations were made to the model, ensuring that subsequent meshing and calculations would not be affected. (1). Some nodal positions should be adjusted to correspond with the actual points of the load application based on the forthcoming loads and constraints. (2). Small holes smaller than the meshing size should be removed to improve the quality of the mesh division. (3). Components from the corn header frame that have little effect on the finite element analysis results, such as the straw holder board and tension frame, should be removed.

3.1.2. Establishment of Finite Element Model

The simplified 3D model was imported into Ansys, with the element size set to 5 mm. The welding relationships between different parts were simulated through nodal coupling [24]. After mesh division, the finite element model comprised 19,957 elements and 20,399 nodes.

3.1.3. Setting of Loads and Constraints

After the corn header is attached to the feeder house, no relative movement occurs between them; therefore, fixed constraints are applied at the interface of the header. The static loads borne by the header frame mainly include the weight of the ear-picking device, the weight of the auger, and the weight of the chopping device. Specifically, the ear-picking device weighs 94.5 kg, the auger weighs 25.1 kg, and the chopping device weighs 61.2 kg. Loads are applied as concentrated and distributed loads based on the actual installation conditions of each component.

The load distribution is shown in Figure 7. At point A, where the header side panel contacts the auger, a concentrated load is applied; at point B, where the header side panel also contacts the auger, a distributed load is applied; at point C, where the corn header side panel contacts the spiral conveyor, a concentrated load is applied; at point D, where the chopping device is installed, a distributed load is applied; and at point E, a tensile load is applied to the front crossbeam of the header frame. The self-weight of the corn header frame is accounted for by setting a downward gravitational acceleration of 9.8 m/s².

3.1.4. Analysis of Static Simulation Results

After completing the aforementioned steps, total deformation and equivalent stress were inserted into the solver module for calculation. The results are shown in Figure 8.

From the total deformation of the corn header frame shown in Figure 8a, it can be seen that the maximum deformation is 0.98 mm. Given that the maximum allowable deformation was set at 10 mm [25], the corn header frame satisfies the stiffness requirements. From the equivalent stress shown in Figure 8b, it is evident that the corn header frame is uniformly stressed, with a maximum stress of 100.9 MPa, which is below the material’s yield strength of 235 MPa. These simulations indicate that the strength and stiffness of the corn header frame meet the material requirements with a considerable margin, suggesting significant potential for optimization.

3.2. Dimensional Optimization Design of the Corn Header Frame

To enhance the safety during the operation of the combine harvester and to reduce the weight of the corn header, eight dimensions were selected as design variables: the thicknesses of the front crossbeam, lower rear crossbeam, upper rear crossbeam, left side panel, right side panel, left longitudinal beam, central longitudinal beam, and right longitudinal beam. The range of thicknesses and dimensions for each component is presented in

Table 2. Range of thicknesses and dimensions for components.

Component Name	Initial Thickness /mm	Lower Limit /mm	Upper Limit /mm
Front Crossbeam	6	3	5
Lower Rear Crossbeam	5	2	5
Upper Rear Crossbeam	5	2	5
Left Side Panel	6	3	5
Right Side Panel	6	3	5
Left Longitudinal Beam	5	2	5
Central Longitudinal Beam	5	2	5
Right Longitudinal Beam	5	2	5

.

3.2.1. Establishment of a Surrogate Model

In this study, a central composite experimental design was utilized to design experiments for the eight design variables, selecting a total of 81 experimental sample points. The accuracy of the response surface model was verified through the coefficient of determination R², with a result closer to 1 indicating higher precision of the surrogate model [26]. As shown in Figure 9, the coefficients of determination for the maximum stress and total deformation of the corn header frame surrogate models were close to 1, suggesting a high reliability of the surrogate models.

3.2.2. Lightweight Design of the Corn Header Frame

The optimization goal was to minimize the mass of the corn header frame, with the maximum equivalent stress and total deformation serving as constraints. The eight component thickness dimensions were used as design variables, mathematically described as follows:

$$\left\{\begin{array}{l}{m}_{\min }\\ s.t.\left\{\begin{array}{l}{\sigma }_{\max }\le 235\mathrm{Mpa}\\ k_{\max }\le 10\mathrm{mm}\end{array}\right.\end{array}\right.$$

(4)

where m represents the mass of the corn header frame, σ_max represents the maximum equivalent stress of the corn header frame, and k_max represents the maximum total deformation of the corn header frame.

The optimization results are presented in

Table 3. Original and optimized dimensions.

Item	Before Optimization	After Optimization	Rounded After Optimization
Front Crossbeam/mm	6	3.6	4
Lower Rear Crossbeam/mm	5	2.0	3
Upper Rear Crossbeam/mm	5	2.9	3
Left Side Panel/mm	6	2.8	3
Right Side Panel/mm	6	2.6	3
Left Longitudinal Beam/mm	5	2.9	3
Central Longitudinal Beam/mm	5	2.7	3
Right Longitudinal Beam/mm	5	2.1	3
Mass/kg	82.6	-	54.2
Maximum Stress/MPa	100.9	-	187.6
Maximum Deformation/mm	0.9	-	5.3

. According to the specifications of steel available on the market, the optimized data were rounded off, and the finite element model was modified accordingly. The maximum equivalent stress of the corn header frame was calculated to be 187.6 MPa, and the maximum deformation was 5.3 mm. The optimized mass was 54.2 kg, representing a mass reduction of 34.2%, indicating significant lightweight effects.

3.3. Validation of Finite Element Model Effectiveness

To verify the accuracy of the corn header frame finite element model established based on the optimized data, modal analysis was performed using Ansys (2021r1) finite element software. Meanwhile, modal testing was also conducted to obtain the natural frequencies of the corn header frame at various modes, and a comparative analysis between the two was carried out.

3.3.1. Modal Analysis of the Cutter Platform Frame Structure

The results of the first six orders of modal analysis of the corn header frame are presented in

Table 4. Natural frequencies of the corn header frame.

Mode Order	First Mode	Second Mode	Third Mode	Fourth Mode	Fifth Mode	Sixth Mode
Frequency/Hz	7.72	17.63	19.76	44.79	47.3	54.94

.

3.3.2. Modal Analysis of the Corn Header Frame Structure

(1)

Modal Testing Equipment and Method

The equipment used for the test was the DHDAS dynamic signal acquisition device produced by Jiangsu Donghua Testing Technology Co., Ltd., which includes an excitation module, data acquisition module, and modal analysis module. To simulate the free state of the corn header frame, it was suspended in the air using elastic ropes. A single-point excitation and multi-point response method was employed for the test. To accurately reflect the vibration characteristics of the corn header frame, 10 measuring points were selected based on the structural outline of the frame.

(2)

Modal Testing Results

The modal testing results are shown in

Table 5. Experimental modal results.

Mode Order	First Mode	Second Mode	Third Mode	Fourth Mode	Fifth Mode	Sixth Mode
Frequency/HZ	7.79	18.44	21.6	45.81	51.51	59.12

.

The testing site is shown in Figure 10.

3.3.3. Comparative Analysis Between Calculated and Experimental Modal Results

The comparison between the calculated modal results and experimental modal results of the corn header frame is shown in

Table 6. Comparative analysis of the modal simulation and experimental modal results.

Mode Order	Calculated Mode	Experimental Mode	Error (%)
first mode	7.72	7.79	0.91
second mode	17.63	18.44	4.59
third mode	19.76	21.6	9.31
fourth mode	44.79	45.81	2.28
fifth mode	47.3	51.51	8.9
sixth mode	54.94	59.12	7.61

. The greatest discrepancy was observed in the third mode, with an error rate of 9.72%. The consistency between the calculated free modal results and the experimental modal results indicates the accuracy of the finite element model of the corn header frame established based on optimized data. The reliability of the static simulation results is confirmed, and the optimized corn header is suitable for manufacturing and production.

4. Field Experiment

After the prototype of the corn header was manufactured, field tests were conducted in Anju District, Suining City, Sichuan Province, to observe the operational performance of the designed corn header and to determine the optimal working parameter combination for the machinery.

4.1. Field Overview

The test field was planted with the corn variety “Zhenghong 507”, with a growth period of 121.1 days. The ears have short stalks, an average of 17.9 rows per ear, and the kernels are medium sized, yellow, and dent shaped. The average row spacing of the corn plants was 400 mm, with an average plant spacing of 115 mm, an average ear height of 950.5 mm, an average stalk diameter of 21 mm, an average plant height of 2492 mm, and a stalk lodging rate of less than 1%. The estimated plant density per hectare was about 55,500 plants. The situation of the corn plants in the field is shown in Figure 11.

4.2. Field Test Plan

4.2.1. Test Design

There are three main factors [27,28,29] affecting the harvest effect and efficiency of the harvester, which are the speed of the combine harvester, the speed of the culm roller, and the water content of the corn grain. As shown in

Table 7. Test factor coding.

Code	Test Factor
	Combine Harvester Travel Speed (m/s)	Stalk Polled Roller Rotational Speed (r/min)	Moisture Content of Corn Kernels (%)
−1	0.8	500	25
0	1.0	575	30
1	1.2	650	35

, the Box–Behnken experimental design method was used to test the above factors using the maize ear loss rate and ear loss rate as indicators where the moisture content of the corn kernels was continuously monitored, and experiments were conducted once the moisture content of the corn kernels met the experimental requirements.

4.2.2. Test Method

For each trial, the length of the harvesting operation area was set to 50 m, including a 30 m test area for the experiment, a 10 m preparation area for aligning and stabilizing the speed of the machinery, and a 10 m deceleration area for stopping the machinery [30]. The data measured for each test group included corn header grain loss and ear loss, with the sum of grain loss and ear loss constituting the total loss of the corn header.

After the harvesting operation, the corn kernels and ears scattered in the field represent the combined loss from the corn header and the threshing and cleaning unit. Since these two types of losses are mixed together, it is not possible to directly measure the loss rate of the corn header separately. To address this issue, a 5 × 15 m plastic tarp was attached behind the combine harvester before the field experiment. This tarp collected all the debris discharged from the rear of the combine harvester during harvesting. After the experiment, the grains and ears scattered on the ground were considered the loss from the corn header. The field harvesting site is shown in Figure 12.

4.2.3. Evaluation Indicators

The experiment used the corn header grain loss rate y₁ and the corn header ear loss rate y₂ as evaluation indicators, as shown in Equation (5) as follows:

$$\left\{\begin{array}{c}{y}_1={\displaystyle \frac{M_{ck}}{M_c}}\\ y_2={\displaystyle \frac{M_{ce}}{M_c}}\end{array}\right.$$

(5)

where M_c is the total mass of grains and ears collected from the ground, g; M_ck is the mass of grains collected from the ground in g; and M_ce is the mass of ears collected from the ground, g.

4.2.4. Results and Analysis

The experimental design and results are shown in

Table 8. Experimental results.

Run	Combine Harvester Travel Speed x1 (m/s)	Stalk Polled Roller Rotational Speed x2 (r/min)	Moisture Content of Corn Kernels x3 (%)	Corn Header Grain Loss Rate y1 (%)	Corn Header Ear Loss Rate y2 (%)
1	1	575	30	0.27	0.97
2	0.8	500	30	0.15	0.64
3	1	650	35	0.25	1.26
4	1.2	575	25	0.48	1.72
5	1	650	25	0.59	1.2
6	0.8	575	35	0.23	0.9
7	1.2	575	35	0.2	1.5
8	1.2	650	30	0.49	1.92
9	1	575	30	0.24	0.94
10	0.8	650	30	0.43	1.36
11	1.2	500	30	0.18	1.58
12	1	500	35	0.19	0.5
13	1	575	30	0.24	1.09
14	1	500	25	0.25	0.92
15	1	575	30	0.34	1.12
16	0.8	575	25	0.43	1.13

.

The data in Table 8 were processed, and a variance analysis was conducted for both corn header grain loss and ear loss, as shown in

Table 9. Variance analysis for corn header grain loss and ear loss.

Sources	Corn Header Grain Loss Rate (%)					Corn Header Ear Loss Rate (%)
	Sum of Squares	df	F-Value	p-Value	Significance	Sum of Squares	df	F-Value	p-Value	Significance
model	0.2508	9	13.27	0.0026	**	2.12	9	38.73	0.0001	**
x1	0.0015	1	0.426	0.526	-	0.9045	1	148.79	<0.0001	**
x2	0.1225	1	34.53	<0.0001	**	0.5513	1	90.68	<0.0001	**
x3	0.0968	1	27.28	0.0002	**	0.0820	1	13.49	0.0104	*
x1 × 2	0.0002	1	0.1071	0.7545	-	0.0361	1	5.94	0.0507	-
x1 × 3	0.0016	1	0.7619	0.4163	-	0.0000	1	0.0041	0.9510	-
x2 × 3	0.0196	1	9.33	0.0224	*	0.0576	1	9.47	0.0217	*
x12	0.0030	1	1.44	0.2753	-	0.4727	1	77.75	0.0001	**
x22	0.0006	1	0.2976	0.6051	-	0	1	0.0010	0.9755	-
x32	0.0049	1	2.33	0.1775	-	0.0150	1	2.47	0.1672	-
residual	0.0126	6	-	-	-	0.0365	6	-	-	-
lack of fit	0.0059	3	0.8876	0.5379	-	0.0131	3	0.5588	0.6778	-
error	0.0067	3	-	-	-	0.0234	3	-	-	-
cor total	0.2634	15	-	-	-	2.16	15	-	-	-

(Note: “*” indicates a significant effect at the 95% confidence interval; “**” indicates a significant effect at the 99% confidence interval.)

.

A multiple regression analysis was performed on the experimental results shown in Table 7 to establish regression equations for the corn header grain loss rate y₁ and ear loss rate y₂ with the combine harvester’s travel speed x₁, the rotational speed of the stalk polled roller x₂, and the moisture content of corn kernels x₃, as shown in Equation (6).

$$\left\{\begin{array}{l}{y}_1=0.273+0.124x_2-0.11x_3-0.07x_2{x}_3\hfill \\ y_2=1.03+0.336x_1+0.263x_2-0.1x_3+0.012x_2{x}_3+{0.344x_1}^2\hfill \end{array}\right.$$

(6)

The p-values of the model from the variance analysis shown in Table 8 were highly significant, indicating that the experimental design was reasonable. The p-values for the lack of fit were greater than 0.05, meaning they were not significant, suggesting that the regression equations fit well with the actual situation and can be used for prediction and analysis of the experiments.

The response surfaces of the interactions between various factors, as shown in Figure 13 and Figure 14, reveal the following insights. As the rotational speed of the stalk rolls increases, both the corn header grain loss rate and the ear loss rate rise due to the increased force of impact between the ears and the ear-picking plates at higher stalk roll speeds. With the increase in kernel moisture content, both the ear loss rate and the grain loss rate of the corn header decrease because the increase in moisture content softens the corn kernels, causing part of the energy from collisions between the corn ears and the ear-picking plates to be absorbed by kernel deformation, thereby reducing the bouncing amplitude of the ears. As the forward speed of the machinery increases, both the grain loss rate and the ear loss rate of the corn header first slightly decrease and then continue to rise; this is because when the machinery’s forward speed is too slow, the feeding stage (period I) speed does not match the speed of the grain chains, and when the machinery’s forward speed is too fast, the small distance between corn plants leads to a large number of corn plants entering the ear-picking device per unit time, making the ear-picking operation more complex and resulting in losses.

4.3. Parameter Optimization and Validation Experiment

To achieve the optimal combination of working parameters for field harvesting, with the goals of minimizing the corn header grain loss rate and ear loss rate, the value ranges of each test factor were used as boundary conditions. The multi-objective optimization module in Design-Expert (11) software was used to solve for the best combination of parameters, which were determined to be a machinery forward speed of 0.94 m/s, a stalk roll rotational speed of 566.5 r/min, and a kernel moisture content of 25%, with a predicted corn header grain loss rate of 0.4% and an ear loss rate of 0.98%.

Field validation tests were conducted based on the optimization results, and the outcomes were a corn header grain loss rate of 0.32% and an ear loss rate of 1.1%, which were essentially consistent with the predicted results.

5. Discussion

The intercropping of soybeans and corn is a farming method that increases yield without expanding the planting area. However, current corn harvesters on the market are designed for standard planting patterns and are not suitable for harvesting corn in soybean–corn intercropping systems. This necessitates the development of specialized corn headers tailored for soybean–corn intercropping. The focus of this article is to develop a header for harvesting high-density corn planted in soybean–corn intercropping configurations.

Soybean–corn intercropping is an agricultural practice that is being promoted, with corn plants spaced 400 mm apart, compared to the usual 600 mm. As such, there is no mature header available on the market specifically for soybean–corn intercropping. When wide-row corn harvesters are used to harvest narrow-row corn, it can result in corn stalks being pushed down or bent, reducing the efficiency of the harvest. Therefore, this article designs a corn header suitable for 400 mm row spacing. To ensure that corn yields do not decrease, the plant spacing within rows is 100–170 mm, more densely planted than the previous 200–250 mm. This requires faster stalk roller speeds, but as the speed of the stem rollers increases, the impact force between the ears and the ear-stripping plates also rises, leading to higher ear and grain loss rates. As the moisture content of the kernels increases, they become softer, absorbing some of the energy from collisions with the ear-stripping plates, which reduces both ear and grain loss rates. With an increase in the forward speed of the machinery, the grain and ear loss rates initially slightly decrease before continuing to rise. The experimental results show that when the machine’s forward speed is 0.94 m/s, the straw rotation speed is 566.5 r/min, the kernel moisture content is 25%, the corn grain loss rate is 0.32%, and the ear loss rate is 1.1%. Compared to existing Jinxing 4LZ-1.6Z headers, the header studied in this article is significantly below national standards, making it more effective for corn harvesting.

The corn header researched in this article is better suited for harvesting corn in soybean–corn intercropping systems, accommodating narrow row spacing and shorter plant spacing within rows.

6. Conclusions

(1)

Based on the characteristics of corn harvesting in the strip intercropping mode of soybeans and corn, the gearbox, ear picker, and corn header frame were redesigned and recalculated. A lighter, lower-loss header specifically designed for the strip intercropping mode of soybeans and corn was developed.

(2)

Finite element software was used to perform static calculations on the designed corn header frame, revealing significant optimization potential. To reduce the overall weight of the corn harvester, the dimensions of the harvester frame were optimized, resulting in a weight reduction of 28.4 kg. The calculated modal results were compared with the experimental modal results, validating the effectiveness of the static calculations for the lightweight corn header frame and providing a reference for actual production.

(3)

The experimental results show that the optimal operating parameter combination for the combine harvester is a forward speed of 0.94 m/s, a stalk roll rotational speed of 566.5 r/min, and a kernel moisture content of 25%. Under these conditions, the grain loss rate of the corn header is 0.32%, and the ear loss rate is 1.1%. These experimental results provide effective technical indicators for subsequent actual production.