Design and Performance Test of Soybean Profiling Header Suitable for Harvesting Bottom Pods on Film

Abstract

In order to solve the problems of bottom pod leakage and soil removal by header, a soybean header profiling system was designed in this paper. The cutter height off-ground detection device was installed on both sides of the header, and the cutter distance from the ground was represented by the angle sensor turning when the profiling wheel met the rolling ground. The hydraulic electromagnetic reversing valve was installed so that the profiling system could automatically control the lifting of the header, the unilateral power of the solenoid valve was 0.15 s, and the height of the cutter from the ground was changed by 10 mm. The height of the cutter off the ground was set to 80 mm, and the adjustment range of the soybean header profiling system was 45–125 mm. The test results showed that the maximum absolute error of the cutter off the ground height detection device was 5.98 mm, the minimum absolute error was 1.00 mm, and the relative error was 0.038. The cutter height adjustment device was powered for 0.15 s, and the average adjustment distance was 11.158 mm. The soybean header profiling system did not shovel soil during field harvest, and the stubble height of 85% of soybean plants was less than 10 mm from the set height after harvest. The results showed that the soybean header profiling system could effectively adjust the cutter height from the ground so that the cutter height from the ground was kept at 80 mm. This study could provide a reference for the intelligent design of soybean harvesters.

1. Introduction

Because of the unique climatic conditions in Xinjiang, soybean needs to be planted with film. The plastic film easily gets entangled in parts such as the blades and rollers of the header, causing the equipment to run inefficiently and potentially damaging it. Additionally, the entanglement and blockage of the plastic film can cause the harvester to frequently stop for cleaning, reducing harvesting efficiency. The position of the soybean bottom pod is low during harvest, and it is difficult for machine operators to accurately judge the field fluctuation and timely adjust the machinery, and thus the problem of bottom pod leakage being caused by an overly high cutter height from the ground and the problem of the header shovel caused by an overly low cutter height from the ground during soybean harvest regularly occur [1,2,3]. The header of a traditional combine harvester cannot meet the demand of soybean harvest, which greatly reduces the quality and efficiency of soybean harvest [4,5,6]. Therefore, the height adaptive adjustment combine harvester came into being. This type of combine harvester integrates harvesting, threshing, and cleaning into one unit [7,8], allowing it to better adapt to the complex terrain of the fields.

Currently, scholars both domestically and internationally have conducted a series of studies on the adaptive adjustment of the header. By designing automatic control systems, real-time automatic adjustment of header height was achieved. These systems possess adaptive adjustment functions, enabling automatic regulation according to different crop and field conditions, thereby improving harvesting accuracy and efficiency [9,10]. Research on the detection of cutter bar height mainly falls into three categories: contact detection, non-contact sensor detection [11,12], and machine vision detection [13,14]. The height adjustment of the header is mainly through the controller to send signals to the hydraulic solenoid valve to control the expansion of the hydraulic cylinder. Douglas designed a hook plate profiling device, the profiling plate is located under the cutter and rotates at an angle after contact with the ground, so as to detect terrain changes [15]. The shearer designed a kind of flexible cutter, the cutter is installed on the header through the spring blade. When the cutter connected with the spring blade touches the ground during harvesting, the compression amount of the spring blade can change with the fluctuation of the ground, so as to realize the function of header profiling [16]. Long proposed an indirect measurement method of header height based on vehicle inclination angle and header inclination angle and developed an adaptive adjusting system of header height based on inclination sensor [17]. Cook designed a set of header height detection devices with a laser sensor, attitude sensor and inclination sensor combined; The detection method of multi-sensor fusion increased the detection accuracy of header height [18]. Haydar developed a machine vision control system based on deep learning to detect fruit height and accurately and automatically adjust the picking position [19]. Li proposed a vegetable ridge height detection method based on image processing technology, high-resolution cameras were used to collect vegetable plot images, so as to conduct subsequent research on walking, adjustment and harvest [20].

Different from inland areas, the stems and leaves of soybeans in Xinjiang are luxuriant during harvest, and the growth characteristics of soybeans increase the difficulty of non-contact sensor detection and machine vision detection. In this study, a pre-contact profiling wheel was designed to detect the height of the cutter from the ground. The detecting device was located in front of the cutter and detects the ground fluctuation in front of the cutter in advance, so that the cutter can adjust its height in time. By installing a hydraulic solenoid valve to control the expansion and shrink of the hydraulic cylinder of the header, the height of the cutting tool from the ground can be changed. The relationship between the electrification time of the solenoid valve and the change of cutter height from the ground was established. The soybean header profiling system designed in this research was designed to adjust the distance between the cutter and the ground, keep the distance between the cutter and the ground stable, and reduce the problems of bottom pod leakage and soil shovel in the harvest process.

2. Materials and Method

2.1. The Composition of Soybean Header Profiling System

In this study, according to the field growth characteristics of Xinjiang soybean, a pre-multi-point contact header profiling system was used. When the header profiling system is working, it needs to first detect the field terrain, calculate the cutter height off the ground, and compare the obtained ground height with the set standard height, so as to adjust the header height and adjust the cutter height off the ground of the soybean harvester by controlling the oil intake and output of the hydraulic cylinder. The working process is shown in Figure 1 [21,22,23,24]. During traditional harvesting, the header height is 30–40 mm above the ground, leading to soil scooping and increasing the difficulty of the harvesting process. To investigate the height of the lowest pods on soybeans planted with plastic film, a test was conducted in the soybean experimental field of the Xinjiang Academy of Agricultural Reclamation Sciences. The height of the lowest pods was measured using the five-point sampling method, with ten groups of tests conducted. The results showed that the average height of the lowest pods was 146.8 mm, although some plants had pods that were significantly lower. Analysis of the test results indicated that over 80% of the soybean plants had the lowest pod height exceeding 80 mm. Using 80 mm as a reference provides a basis for determining the height of the cutting blade above the ground in the subsequent discussion.

Based on the analysis of the working flow of the header profiling system, this study designed a soybean header profiling system that includes a cutter height off-the-ground detection device, cutter height off-the-ground information processing system and cutter height off-the-ground adjustment device. The composition of the whole profiling system is shown in Figure 2. When harvesting in the field, the contour wheel is close to the ground, and the change in the terrain will cause the angle sensor at the end of the contour device to change the Angle. The sensor value is sent to STM32, and the real-time ground height of the cutter is calculated by the relation between the angle and the cutter height. The cutter height from the ground is compared with the set height to determine the working mode and working time of the solenoid valve. STM32 controls the on–off mode and time of the solenoid valve through the relay, so as to adjust the expansion of the hydraulic cylinder and change the height of the cutter from the ground.

2.2. Cutter Height off the Ground Detection Device Design

Aiming at the design requirements of the ground height detection device of the header proposed above, this study designed a front wheel cutter ground height detection device, its specific structure is shown in Figure 3. The device is fixed on both sides of the header of the harvester by bolts, and the angle of the support rod where the contour wheel is located changes when the height of the field terrain changes. The whole header height off the ground detection device is V-shaped, which is different from the height detection device with a straight bar in front of the contour wheel. The height detection device designed in this research is subject to less ground resistance during field harvest, so as to avoid the phenomenon of “earth pushing” caused by the contour wheel during operation, and increase the service life and working stability of the device [25,26]. A limit protection device is installed between the profiling rods to restrict the measurement range of the ground height and provide a level of protection for the detection device and the header in cases where the terrain relief exceeds the measuring and adjusting range [27,28,29].

The height of the ground detection device consists of two steel plates 500 mm long, 100 mm wide and 10 mm thick and two steel plates 125 mm long, 100 mm wide and 10 mm thick welded into the main frame of the device. Four bearing seats with an inner diameter of 20 mm are installed to realize the function of rotation of the central axis where the angle sensor and limit protection device are located. Among them, the distance between the center position of the rotating shaft where the angle sensor is located and the right baffle is 180 mm, the distance between the center of the rotating shaft of the angle sensor and the rotating shaft of the limit protector is 277 mm, and the distance between the rotating shaft of the limit protector and the left baffle is 90 mm. The profiling wheel is connected with the angle sensor rotating shaft through a steel plate with a length of 250 mm, a width of 30 mm and a thickness of 10 mm. The profiling wheel is a nylon wheel with a radius of 52 mm and a thickness of 50 mm. The specific size of the ground height detection device and the installation position of each component are shown in Figure 4.

2.3. The Relationship between the Height of the Cutter from the Ground and the Angular Momentum

When the ground height detection device of the front wheel header designed in this study meets the undulating ground in the harvest process, the angle between the profiling bar and the horizontal plane will change, and the angle sensor will convert the angle change into an electrical signal and transmit it to the control system for analysis and processing. As shown in Figure 5, the soybean harvester encountered A raised ground when advancing from point A to point B, and the height difference between point A and point B was $\Delta H$.

At this time, the angle between the contour bar and the horizontal plane, and the vertical distance between the angle sensor and the center of the contour wheel change and decrease to ${\theta }^{\prime }$ and ${h_2}^{\prime }$. According to the geometric relationship in the figure, the relationship between the vertical distance between the angle sensor and the center of the contour wheel, the angle between the contour bar and the horizontal plane, and the length of the contour bar at point A can be obtained as follows:

$$h_2=l\mathrm{s}\mathrm{i}\mathrm{n}\theta$$

(1)

By analyzing the geometric principle of the ground height detection device of the soybean header, the expression of the ground height of the angle sensor at point A can be obtained:

$${h=h}_2+h_1=l\mathrm{s}\mathrm{i}\mathrm{n}\theta +r$$

(2)

The soybean harvester works from point A to point B, and the height difference between two points A and B is $\Delta H$, according to the theoretical analysis, the $\Delta H$ value is equal to the vertical distance between the angle sensor and the center of the profiling wheel at point A minus at point B, that is, the height difference between two points A and B is:

$$\Delta h=h_2-{h_2}^{\prime }=l(\mathrm{s}\mathrm{i}\mathrm{n}\theta -\mathrm{s}\mathrm{i}\mathrm{n}{\theta }^{\prime })$$

(3)

where: $l$ is the length of the profiling rod, mm; $\theta$ is the angle between the profiling bar and the horizontal plane; $r$ is the radius of the copying wheel, mm.

Therefore, the distance between the cutter and the ground of the soybean harvester can be expressed in real-time through the angle between the profiling bar and the horizontal plane. Before field harvesting, the cutter’s height off the ground should be manually adjusted to 80 mm before harvesting. At this time, when the profiling wheel meets the undulating ground in the field, the angle sensor will produce A difference according to the detection principle in Figure 5. At this time, the change in the cutter’s height off the ground is the height difference between points A and B in the figure, and the cutter’s height off the ground is equal to $(80 - \Delta h)$ mm. At this time, the height of the cutter from the ground H is:

$$H=80-\Delta h=80-l(\mathrm{s}\mathrm{i}\mathrm{n}\theta -\mathrm{s}\mathrm{i}\mathrm{n}{\theta }^{\prime })=80-320(\mathrm{s}\mathrm{i}\mathrm{n}\theta -\mathrm{si}n{\theta }^{\prime })$$

(4)

2.4. Header Hydraulic System Modification

In order to meet the requirements of up–down adjustment during the operation of the soybean profiling header [30,31,32], the single-acting hydraulic cylinder of the header was replaced with a double-acting hydraulic cylinder [33,34]. In this study, we used Yanmar AW82G combine harvester to produce a soybean profiling header. The hydraulic oil in the hydraulic system of the original header flows from the oil tank to the hydraulic control valve of the header through the hydraulic pump. The valve is an integrated valve, that can respectively control the lifting of the header, the steering of the body and the lifting of the rotary wheel. Figure 6 is the Yanma AW82G combine header hydraulic control valve, as shown in the figure: No. 4 tubing is connected to the hydraulic pump, No. 5 tubing is connected to the oil tank; the No. 1 oil pipe on the far right is connected to the cutting platform lifting oil cylinder, and the lifting of the header is adjusted by the front and back displacement of the control handle; No. 2 and No. 3 tubing are connected with the steering hydraulic actuator, and the left and right movement of the control handle is used to adjust the left and right steering of the harvester. The No. 6 oil pipe is connected to the lifting cylinder of the rotary wheel, and the height of the rotary wheel is adjusted by pushing the button on the handle.

In order to realize automatic adjustment of the header height of the soybean harvester, the hydraulic system of lifting and lifting of the header is modified based on the Yanma AW82G combine harvester. Firstly, the original single-acting hydraulic cylinder of the header is replaced with a double-acting hydraulic cylinder, and then the manual valve that controls the lifting of the header is replaced with a three-position four-way solenoid valve. A pressure regulating valve and a throttle valve are installed between the hydraulic cylinder and the three-position four-way solenoid valve. The pressure regulating valve plays the role of constant pressure and regulating pressure in the hydraulic system of the header height. The throttle valve regulates the flow of hydraulic oil in the hydraulic line by adjusting the throttling section/length. In the subsequent work, the amount of oil in and out of the hydraulic cylinder per unit of time can be changed by adjusting the pressure regulator and throttle valve. The hydraulic system for the height of the header after modification is shown in Figure 7.

In addition to ensuring the stability of the hydraulic system, the pressure regulator and throttle valve can also regulate the pressure and flow rate of the hydraulic oil circuit by adjusting the pressure regulator and throttle valve. This allows for the adjustment of the cutter’s height during rising and falling after the solenoid valve is energized within a specific time frame. Through the adjustment of the pressure regulator and throttle valve in this study, the hydraulic system for cutter height adjustment can provide power to the solenoid valve within 0.15 s, resulting in a 10 mm change in the cutter height from the ground.

2.5. Cutter Height off the Ground Adjustment Control Strategy

The header height adaptive control system mainly consists of three parts: an information acquisition input module, a processor module and a control output module. The information acquisition module is composed of a cutter height detection device. The profiling bar changes the angle according to the fluctuation of the ground. The angle sensor transmits the angle change to the processor module by electrical signal. The processing module selects STM32F407ZGT as the processor, which is responsible for receiving the signal transmitted by the angle sensor, then processing the electrical signal into the angle of the profiling rod rotation, and calculating the angle according to the detection principle to obtain the current ground height of the cutter, and finally adjusting the hydraulic cylinder expansion capacity according to the control plan by outputting the electrical signal [35,36,37,38]. The structure block diagram of the whole control system is shown in Figure 8. The entire control process of the cutter height adaptive adjustment system is as follows: The profiling wheel contacts the field ground, and the output signal of the angle sensor changes with the undulations of the ground. Upon receiving the signal sent by the sensor, the processor parses the current angle value and calculates the cutter’s ground clearance when it reaches the position of the profiling wheel. Based on the control strategy, the processor energizes the relay, thereby driving the solenoid valve core to operate, causing the hydraulic cylinder to extend or retract, and thus adjusting the cutter’s ground clearance.

The cutter height adjustment system uses an ADC (Analog-to-Digital Converter) to convert the analog signals collected by the angle sensor into digital signals. The STM32 processes and calculates the digital signals from the angle sensor to obtain the current angle between the profiling rod and the horizontal plane. This angle “θ” is then substituted into the cutter ground clearance calculation formula to determine the current distance between the cutter and the ground. The STM32 compares the current cutter ground clearance with the system’s set ground clearance. If the difference is within the adjustment threshold of the target height, the STM32 does not adjust the hydraulic cylinder’s extension or retraction. When the difference exceeds the adjustment threshold of the target height, if the difference “>0”, the cutter ground clearance is too large, leading to missed cuts at the bottom pods. Therefore, the hydraulic cylinder extension is reduced to lower the cutter height. Conversely, if the difference “<0”, the cutter ground clearance is too small, causing the cutter to dig into the soil and resulting in “muddy faces” on the harvested soybeans. In this case, the hydraulic cylinder extension is increased to raise the cutter height.

In this study, multi-point detection is used for the soybean profiling header, and the cutter height detection device is installed on both sides of the header. When harvesting in the field, because of the slope of the ground and the softness of the soil, the cutter height detected by the profiling wheel on both sides will be inconsistent. In the face of this situation, the cutter height off the ground adjustment system gives priority to ensuring that the header does not shovel soil, that is, the value of the lower ground height output by the system is used as the current cutter height off the ground. The specific control principle of the cutter height off-the-ground adjustment system is shown in Figure 9.

The control principle of the soybean cutter ground height adjustment system is to make a difference between the measured cutter ground height and the set cutter ground height, and determine which side of the solenoid valve is powered and the time of power through the difference. In this study, the cutter height from the ground is set to 80 mm, floating 5 mm up and down as the set height interval, that is, when the cutter distance from the ground is 75 mm to 85 mm, the cutter height adjustment system does not work. When $H - H_0$ is greater than 5, the height of the cutter from the ground is >85 mm, the cutter should be adjusted downward, and the cutter height adjustment system controls the hydraulic cylinder shrinkage; When $H - H_0$ is less than 5, the height of the cutter from the ground is <75 mm, the cutter should be adjusted upward, and the cutter height adjustment system controls the hydraulic cylinder elongation.

Considering that the distance between the cutter and the ground is 35 mm when the header touches the ground, the adjustment interval is set to the rising interval of 45 mm–75 mm and the falling interval of 85 mm–125 mm. The interval is divided into several cells by 10 mm, and each interval corresponds to a different solenoid valve power-on time. Since the hydraulic response is adjusted to power up 0.15 s, and the header rises/falls 10 mm, the power-up time of each adjustment interval is determined. The specific control principle of the adjustment system is shown in Figure 10, the partial code is shown in Figure 11.

According to Formula (5), the angle measured by the sensor is converted into the height of the cutter from the ground, which is of great significance for the subsequent test verification and comparison. Therefore, this paper uses PyCharm software on a PC to complete the reading of the angle sensor convert the angle into the height, and complete the judgment and selection of the detection height at both ends of the header in PyCharm. Finally, output the cutter height to STM32. In comparison to STM32, PyCharm allows for the direct recording of the ground height of the cutter after each detection, providing convenience for this study in documenting the cutter’s height above the ground. Subsequent adjustments to the cutter’s height are carried out using STM32. The setup of the upper PC and lower STM32 on the soybean harvester is illustrated in Figure 12.

3. Results

3.1. Accuracy Test of Ground Height Detection Device

The cutter height off the ground detection device is the first step of the whole profiling system. If there is a large error between the cutter height off the ground measured by the height detection device and the actual height, the working performance of the profiling system will be seriously affected. In this experiment, the detection accuracy of the cutter height from the ground detection device was tested. The cutter distance from the ground was changed by the key switch on STM32, and the angle sensor was connected to the host computer. The real-time cutter height from the ground value was obtained by reading the sensor angle through PyCharm and compared with the actual cutter distance from the ground measured by the tape measure. The specific process is shown in Figure 13.

3.2. Hydraulic Response Accuracy Test of Cutter Height Adjusting System

After the accurate detection of the cutter height from the ground, whether the cutter height adjustment device can accurately adjust the cutter height to the set interval is of particular interest. In this test, the key switch is used to control the rise and fall of the cutter. On the key, the cutter rises, and under the key, the cutter falls, and the primary solenoid valve of the key is energized by 0.15 s. The initial position of the cutter is 80 mm from the ground. When the height of the cutter from the ground exceeds 140 mm, the key is lowered. When the height of the cutter from the ground reaches 45 mm, the key is lifted. Finally, the cutter reaches the initial position.

3.3. Field Harvest Experiment of Profiling System

In order to further test the working performance of the soybean header profiling system designed in this research institute, the soybean experimental field of Xinjiang Academy of Agricultural and Reclamation Science was selected as the test site to carry out field harvest experiments on the soybean header. The soybean harvest experiment was carried out on the conventional header first, and then the soybean harvest experiment on the profiling header was carried out to compare the soybean harvest effect in the field with or without the profiling system. The results of the experiment were based on the stubble height of the soybean and whether the header was shoveled or not. Each group of test harvesters worked for 60 m. After harvesting, the stubble height was measured every 1 m in the 60-m harvest area, and the stubble height of 60 sampling points was collected in total.

4. Discussion

4.1. The Results of the Accuracy Test of the Ground Height Detection Device

Three groups of precision tests were carried out, respectively. Each group of tests took the landing of the header as the starting position. When the header fell to the ground, the cutter of the header was 35 mm away from the ground, and the header was raised through the key switch. The actual distance and calculated distance of the cutter from the ground obtained by the three groups of tests are shown in Figure 14. It can be seen from Figure 14 that in the three groups of precision tests, the calculated distance of the height detection device has a small deviation from the actual distance of the cutter.

4.2. The Results of the Hydraulic Response Accuracy Test of Cutter Height Adjusting System

After the precision test of the hydraulic height adjustment system of the header is completed, the cutting tool adjustment height of each time is obtained by making the difference of the cutter height from the ground after two adjacent adjustments, and the adjustment distance of the hydraulic system is calculated. The test data are drawn as a graph, and the actual adjustment distance is compared with the set 10 mm adjustment distance. The test results of the three groups are depicted in Figure 15, Figure 16 and Figure 17. During the precision test of the hydraulic height adjustment system for the three header groups, the adjustment height fluctuates around 10 mm, with a maximum adjustment distance of 14 mm and a minimum adjustment distance of 7 mm. The average adjustment distance of the three groups of tests is 11.1579 mm, 11.1053 mm, and 10.7895 mm, respectively, which has a small deviation compared with the set adjustment distance of 10 mm.

4.3. The Results of Field Harvest Experiment of Profiling System

Soybean field harvest experiments were carried out without and with the profiling system, respectively, and the field conditions after the experiments are shown in Figure 18 and Figure 19. The test results showed that the field stubble height changed greatly after the harvester harvest without the profiling system. The field stubble height after the two tests was recorded and plotted into a graph, as shown in Figure 20. The maximum difference between the recorded stubble height and the set height of 80 mm was 50 mm. The stubble height in the field after harvest of the harvester with the profiling system changed little compared with that without the profiling system. In the test, the maximum difference between the stubble height and the set height of 80 mm was 26 mm, and the data within 10 mm of the set height accounted for 85% of the data in this set, indicating that the hydraulic height adjustment system of the header could effectively adjust the cutter height from the ground. Keep the cutter height from the ground at about 80 mm. The phenomenon of soil shoveling occurred during the harvest of the header.

5. Conclusions

(1) A low loss profiling system of a soybean header was designed, which consisted of a measuring device of cutter height off the ground, a hydraulic adjusting system of cutter height off the ground and an adaptive adjusting system of cutter height off the ground, so as to reduce the phenomenon of bottom pod leakage and shoveling of header and keep the cutter height off the ground relatively stable.

(2) In order to represent the change of cutter distance from the ground by the angle of the profiling wheel, the mathematical expression of angle and cutter distance from the ground was established. The single-acting hydraulic cylinder of the header of the harvester was replaced with a double-acting hydraulic cylinder, and the rise and fall of the header are controlled by the hydraulic solenoid valve. The solenoid valve is energized by 0.15 s, and the cutter of the header rises/falls by 10 mm. When the cutter distance from the ground was set to 80 mm, the control method of the soybean header profiling system was determined when the cutter distance from the ground was 45–125 mm.

(3) The accuracy test of the cutter height off-ground detection device and cutter height off-ground adjustment system was carried out. The test results showed that the maximum absolute error between the calculated distance and the actual distance was 5.98 mm, the minimum absolute error was 1.00 mm, and the relative error was 0.038. In the hydraulic response accuracy test of the cutter height off the ground adjustment system, the solenoid valve was energized by 0.15 s, and its adjustment height fluctuated up and down around 10 mm. The maximum adjustment distance was 14 mm, the minimum adjustment distance was 7 mm, and the average adjustment distance was 11.1579 mm.

(4) A field harvest test was conducted on the soybean header profiling system. In the test, there was no shoveling of the header. The maximum difference between the stubble height and the set height of 80 mm was 26 mm, and the data within 10 mm of the set height accounted for 85% of the data sample, indicating that the hydraulic height adjustment system of the header could effectively adjust the cutter height from the ground. Effectively, the cutter height should be at about 80 mm from the ground.