Design and Testing of a New Bionic Corn-Ear-Picking Test Device

Abstract

A new bending fracture principle is proposed for ear picking by simulating the process of manually breaking off corn cobs. Based on this, a new test device for corn ear picking was designed to obtain the relationship between the ear-picking rate and the rotational speed of the snapping rollers, as well as the feeding speed. A mechanical test was conducted on corn at two different harvesting stages. This proved that the tensile breaking force used in ear picking was considerably greater than that associated with bending fracture, regardless of whether it was silage or mature corn. Moreover, the feasibility of the working principle of the bending fracture was tentatively verified by a verification test. Then, ear picking could be achieved using the designed device with less damage occurring to the corn ears and straw, according to the test for corn ear picking. Finally, a range analysis showed that the highest ear-picking rate could be obtained by the test device at a snapping roller rate of 780 r/min and a feeding speed of 1.5 (m/s), with a 40° angle between the snapping rollers and conveyor. Thus, this study provides a reference for the further development of a corn harvester for silage.

1. Introduction

In recent years, with the change in people’s dietary structure, there is a demand for food that is not only delicious, but also health conscious. Fresh corn has gained popularity because of its high nutritional value [1,2]. At the same time, it has earned a reputation as being “value added” because of its higher economic value compared to regular corn [3,4,5]. In order to ensure the taste, fresh corn must be picked within a very short harvest period [6]. However, due to its high moisture content, the existing machinery in the harvesting process very easily causes damage to the cob, and this affect the taste and even causes mildew [7,8,9,10]. As a result, a large part of the corn is still picked manually, limiting the planting scale. Therefore, there is an urgent need for a harvesting machine suitable for fresh corn cob picking to be applied in mechanized operations [11,12].

At present, the harvesting operation of fresh corn is still dominated by the application of common corn harvesters [13]. The core components for the purpose of picking ears are mostly based on two working principles, one of which is to use two relatively rotating picking rollers to restrict the passage of the corn cob through the rubbing and squeezing of the stalk and cob to achieve the picking of ears [14], as shown in Figure 1a. The amount of power consumption of the cob picking device using this principle is high, and the problem of cob gnawing is more serious, especially for fresh corn, where the kernels become pulpy inside and breakage directly reduces the quality of the corn [15]. Another type is the combination of the picking plate and stalk pulling roller, which involves using the stalk pulling roller to block the corn cob and achieve corn picking by stretching and squeezing the stalk, as shown in Figure 1b. Although the damage to the corn cob rubbing is reduced, due to the high water content and toughness of the stalks and outer bracts of fresh corn and the non-adjustable gap between the stalk pulling roller and the picking plate during harvesting, it is very easy for it to cause blockages and affect the efficiency rate [16]. In summary, two ways of picking corn ears can be achieved by applying a forceful stretching action between the corn ears and stalks that exceeds the connection force between them [17], both of which are relatively energy consuming. Both of them are not suitable for fresh corn picking operations because of the limitations of their operating principles.

In order to solve the above problems and find a suitable method for fresh corn picking, a method of picking corn that imitates the manual breaking of corn is proposed. In addition to being applicable to the physical characteristics of fresh corn and reducing the amount of picking damage, this method can significantly reduce the energy consumption during the picking process, and it can preserve the intact corn stalks for full-scale corn harvesting. In addition, to verify the feasibility of the proposed method, mechanical experiments were conducted to compare with the tensile picking principle used by most current harvesters to prove the rationality of the proposed method. Moreover, a fresh corn picking test stand was designed based on this principle, and the optimal operating parameters of the test stand were obtained by orthogonal and Box–Behnken tests.

2. Materials and Methods

2.1. Mechanical Tests on Corn Ear Breaking

2.1.1. Comparison of Two Different Methods Used in Corn Ear Picking

Fresh corn is easily damaged by external forces because of it has a high moisture content and the internal material of the kernels is pulpy, resulting in the corn ears having low mechanical strength [7,18]. However, during manual harvesting, the corn is rarely damaged because the process of hand picking follows the growth pattern of the corn. The corn ears naturally droop after maturity, and the moisture content and mechanical strength of the peduncle gradually decrease until it breaks, at which point the corn ears drop [19,20]. During the process of hand picking, the force exerted by the human hand on the corn is the same as that of gravity.

When the corn ear is squeezed, an upward tensile force is exerted by mechanized harvesting, while when it is held by hand, a vertical downward bending force is applied. The two methods of force are obviously different. In order to find a suitable operation for fresh corn picking, we compare the two methods by performing a mechanical test.

2.1.2. Test Materials

The corn variety used in the picking test was MF12; it was bred by the Jilin Breeding Experimental Station in Liuhe county, Jilin province of China. It is widely grown in the northeastern China. In addition, to verify the effects of corn moisture content on the force mechanism, the corn used for the test were collected in early September 2021 and late October 2021 at Jilin University Agricultural Experiment Base (43°56′46″ N, 125°14′52″ E), when the fresh corn was in the late milk ripe period (corn with an average moisture content of 75 ± 5%) and the mature period (corn with an average moisture content of 15 ± 5%).

A WDW-20 microcomputer equipped with an STC-100 sensor was used to control the electronic universal testing machine and the self-made corn mechanics supporting fixture in order to analyze the effects of the tension and pressure on the corn, as shown in Figure 2.

2.1.3. Measuring Methods

In the tensile mechanical test using the corn ears, a specially made lower fixture was fixed to the loading stage of the universal testing machine, and the upper fixture was equipped with a sensor on the same machine. Then, a corn plant was placed between the upper and lower fixtures. Next, the longitudinal axis of the corn ear was aligned with the center line of the sensor by adjusting the fixture position. This ensured us to ensure the accuracy of the measurement results, as shown in Figure 3a. When the movable plate of the universal testing machine moved upward at a uniform speed, the tensile fracture forces could be measured as the corn ear separated from the straw. Corn from two different harvest periods were measured and put into 35 groups of experiments, which were repeated in each period.

As can be seen from Figure 3b, the specially made lower fixture was fixed during the loading stage of the universal testing stage, while the upper one was connected to the sensor during the mechanical test of the bending force of the corn ear. During the test, the movable plate of the universal testing machine moved downward at a uniform speed, which was similar to the force applied to the corn during manual breaking. The lower end of the corn straw was fixed using a downward bending force applied on the upper surface of the corn ear by the movable rod of the upper fixture. Moreover, data were measured on the bending fracture force of the corn ear which was separated from the straw, and there was a 10 cm horizontal distance between the stressed position of the corn ear and the fixed position of the straw. Corn from two different harvest periods were measured, with there being 35 groups of experiments, which were repeated in each period.

2.2. Test Results and Analysis

The results of the test data are shown in Figure 4. Due to the fibers connecting the ear and the corn stalk, when the peduncle was subjected to both the bending and twisting forces, the force value would continue to grow. When the force reached the breaking point, the value decreased rapidly to 0, at which point the corn ears dropped. Stretching fracture and bending fracture tests were performed on the corn peduncle. The tests results showed that when the fresh corn was at late milk ripe period, the fracture force of the corn peduncle in forward stretching had a range of 301.36 N–701.53 N, with an average value of 456.43 N. The fracture force, when the corn was subjected to bending, was 31.17 N–114.5 N, with an average value of 51.86 N. When the corn was in the mature period, the fracture force of the corn peduncle in forward stretching had a range of 166.23 N–384.95 N, with an average value of 278.80 N. The fracture force when the corn was subjected to bending was 19.28 N–65.43 N, with an average value of 38.50 N (Figure 5). It can be seen that greater forces were required for harvesting fresh corn with a high moisture content than those for mature corn with low moisture content. This is because straw with a high moisture content can be regarded as a plastic material, whereas straw with a low moisture content can be regarded as a brittle material. Based on this, the flexibility of the straw can be weakened, and its brittleness can be enhanced, so the breaking force will be significantly reduced. Moreover, whether the fresh corn or the mature corn, the force required to break corn peduncle by reverse bending was much lower than that for forward stretching, and the force was reduced by about 90%.

Due to a large force being exerted on corn by stretching, it is not suitable for fresh corn. A method of picking corn that imitates the manual breaking of corn is proposed, and a fresh corn picking test stand was designed based on this principle. In addition to it being applicable regardless of the physical characteristics of the fresh corn and reducing the amount of picking damage, this method can significantly reduce the energy consumption during the picking process, and it can preserve the intact corn stalks for a full-scale corn harvesting.

3. Design of Key Components of a New Bionic Test Device for Corn Ear Picking

3.1. Structural Composition

The mechanical experiments were conducted to compare with the tensile picking principle used by most current harvesters to prove that the bionic reverse picking is an excellent method with low force requirements and low power consumption levels, thus supporting the proposed method. Moreover, a fresh corn picking test stand was designed based on this principle.

As shown in Figure 6, the new bionic device for corn ear picking had a frame made of angle steel and a compact structure. The device was composed of a clamping conveyor, left and right snapping rolls, a tension sprocket, an adjusting frame, a frame, and an adjustable speed motor. The clamping conveyor consisted of a conveying belt, a driving wheel, and fixed and movable tension rollers. It was installed at a certain angle in relation to the ground surface. Additionally, there was a certain gap between the two snapping rollers, which were installed symmetrically under the clamping conveyor. The angle between the snapping rollers and the clamping conveyor can be adjusted using the adjusting frame. In addition, the speed of the whole device can be adjusted using three motors.

3.2. Working Principle

The bending fracture was adopted as the working principle for the new bionic corn-ear-picking device because it imitates manual corn breaking. The straw above the corn ear was held by the clamping conveyor, which simulates a human hand. The clamping gap can be automatically adjusted by the fixed and movable tension rollers, based on the straw diameter, during the clamping and conveying period. A corn ear can be picked by means of the bending fracture, which is applied by the snapping rollers. This simulates manual corn ear breaking when two snapping rolls are positioned above the corn ear. During the operation, the corn plants were conveyed by the clamping conveyor to the rear of the snapping rollers. The corn ears gradually made contact with the snapping rollers and were subjected to the bending force, which has a downward incline. Clearly, the corn ears were picked, as each ear was subjected to the bending force. Because a small amount of damage was sustained by the corn straw due to the device, complete straw recycling can also be realized.

3.3. Parameter Design for Key Components

3.3.1. Design of Clamping Conveyor

Because the ear-picking device was a fixed test bench, a clamping conveyor should be designed to drive the movement of corn plants with the purpose of simulating the field operation of the machine. There are three design purposes: (i) the corn plants must be held and transported obliquely to the rear of the machine; (ii) the corn straw must not fall or be clamped, with the guarantee of clamping force being applied during the ear-picking process; (iii) the favorable trafficability of the corn straw must be ensured, so as to prevent blockages occurring.

Based on Figure 7, the left and right clamping frames were designed to satisfy the requirements of the clamping conveyor. The left clamping conveyor frame was equipped with six fixed tension rollers, whereas the right one was equipped with six movable tension rollers to prevent the conveyor belt from loosening during transmission. Specifically, the amount of tension was determined by a tension spring on the staggered left and right rows of the tension rollers. The tension clamping gap can be automatically adjusted in line with the straw diameter during conveying.

3.3.2. Design of Snapping Roller

The ear-picking roller as designed for: (i) picking corn ears regardless of their growth in different directions; (ii) picking corn ears despite their different scion heights; (iii) achieving the backwards transportation of the corn straw; (iv) preventing the straw from being damaged during the process.

Thirty MF 12 corn plants were randomly selected to measure the parameters of their actual growth, and the measurement results are shown in

Table 1. Growth parameters of corn plants.

Parameter	Statistics
	Max	Min	Average	Standard Deviation
Scion height (mm)	1526.3	986.3	1234.11	175.07
Corn ear length (mm)	212.1	169.2	198.18	12.78
Corn ear root diameter (mm)	57.9	44.7	53.13	4.16
Top diameter of corn ear (mm)	22.5	14.2	18.575	2.29
Straw root diameter (mm)	32.9	25.6	30.13	2.15

. According to these actual growth characteristics, the left and right snapping rollers were designed with a 30° adjustment range to pick corn ears with different scion directions and scion heights.

Each snapping roller was designed with spiral grooves to prevent blockages caused by the accumulation of straw during the harvesting process. More importantly, the rotational direction of a snapping roller was determined according to the geometry of its spiral groove. Thus, the corn straws can be transported backwards. Additionally, the respective speeds of the left and right snapping rollers were controlled by the application of two motors to allow different speeds to be studied. The working modes of the snapping rollers and motors are shown in Figure 8.

Figure 9 shows a design sketch of the snapping rollers. Because their average height was 1234.11 mm, based on the measurement results, the working range between the snapping rollers and the clamping conveyor should be at least 260 mm. Additionally, the length of a snapping roller should meet the following requirements:

$$L=\frac{a}{sin15°}$$

(1)

where L is the length of the snapping roller in mm and a is the working range in mm.

Here, a is taken as 260 mm, so the length L of the snapping roller is roughly 1005 mm. To prevent ear picking from being performed when the corn ears enter the groove, d shall satisfy:

$$d_{j\max }<d<d_{s\min }$$

(2)

where d_jmax is the maximum diameter of corn straw in mm and d_smin is the minimum diameter of the corn ear root in mm.

According to Table 1, the maximum diameter of a corn straw was 32.9 mm, and the minimum diameter of a corn ear root was 44.7 mm. Therefore, the groove width d was selected to be 40 mm.

4. Performance Tests with the Ear-Picking Test Table

4.1. Test Equipment and Materials

After the steps of the theoretical analysis were completed, the 3D model construction, ANSYS simulation and optimization, 2D drawing, parts processing, assembly, and debugging steps began. The new bionic corn-ear-picking test device is shown in Figure 10.

After the prototype was assembled, the clamping force of the clamping device was adjusted using a HP-500 tensiometer (measuring range −500~500 N, accuracy 0.1 N). Based on the mechanical experiments the effective clamping force for the clamping chain was calculated to be greater than 65.43 N. By changing the position of the adjusting nut of the spring on the clamping chain, the preload force of the spring on the clamping chain was changed to ensure that the clamping force at each position that was measured was greater than 65.43 N.

The new self-developed bionic device for corn ear picking featured left and right snapping rolls and three motors that controlled the clamping conveyor. The three motors were controlled by three frequency converters with a frequency modulation range of 0–50 Hz and a power range of 4–5.5 kW. In order to test the speed adjustment range and speed stability of the snapping rolls, the DT-2234B photoelectric tachometer had a measurement range of 2.5–99,999 r/min.

4.2. Test Methods

The performance of the ear-picking device could be affected significantly by the speed of the corn feeding and the snapping rollers, as well as the angle between the snapping rollers and the clamping conveyor. Therefore, a three-factor and three-level test was undertaken to evaluate the performance of the ear-picking device.

The ear-picking device was designed with 30°, 40°, and 50° angles between the snapping rollers and the clamping conveyor. Because the range of 0.8–2.5 m/s is generally accepted as the field operation speed of a corn harvester, 1.0, 1.5, and 2.0 m/s were taken as the corn-feeding speeds in the test. The single-factor test was carried out at speeds of 420–900 r/min. As shown in the test results, the goal of ear picking could be achieved at a speed of 420 r/min, with no significant improvement to the ear picking. This was due to the long picking duration. When the speed of snapping rollers reached 900 r/min, although the frame vibrated, the efficiency of the ear picking improved. Therefore, 540, 660, and 780 r/min were selected as the snapping roller speeds, with full consideration given to the working efficiency and safety factors. An orthogonal experiment of three factors and three levels was carried out with 40 corn plants, which made up a group. Thus, the influence of the three factors on the picking process was determined. The levels and factors of the test are shown in

Table 2. Experimental factors and levels.

Level	Factors
	Rotational Speed (r/min)	Feeding Speed (m/s)	Angle (°)
1	540	1.0	30
2	660	1.5	40
3	780	2.0	50

.

Based on these results, the functional relationship between each factor and the ear-picking rate could be further clarified. A partial orthogonal regression analysis was conducted using the test data. The analysis scheme is shown in

Table 3. Part of orthogonal regression experimental design method.

No.	Factors
	1(A)	2(B)	3(C)	4
1	1	1	1	1
2	1	2	2	2
3	1	3	3	3
4	2	1	2	3
5	2	2	3	1
6	2	3	1	2
7	3	1	3	2
8	3	2	1	3
9	3	3	2	1

A’ is the rotational speed of the snapping roller, ‘B’ is the feeding speed of corn, and ‘C’ is the angle between the snapping rollers and clamping conveyor, as described below.

:

4.3. Data Sorting and Detection Indicators in the Early Stage of the Test

In the test, a corn plant moved forward with the rotation of the clamping conveyor. Because the clamping conveyor was installed at an angle of 15° from the horizontal plane, the feeding speed of a corn plant can be calculated as

$$v_x=\frac{\pi dn\cos 15°}{60}$$

(3)

where ν_x is the feeding speed of the corn plant in m/s, n is the speed of the clamping pulley in r/min, and d is the pulley diameter in m.

The ear-picking and grain damage rates were taken as the detection indicators and the ear-picking rate was

$$Y_i=\frac{N_g}{N}\times 100\%$$

(4)

where Y_i is the corn-ear-picking rate in per cent, N_g is the number of picked corn ears in plants, and W_z is the total number of test corn ears.

Additionally, the ear loss rate is expressed as

$$S_u=\frac{W_u}{W_z}\times 100\%$$

(5)

where S_u is the ear loss rate in per cent, W_u is the mass of lost ears after threshing in kg, and W_z is the total grain mass in kg.

4.4. Test Results

The results of harvesting 360 corn plants from nine groups of experiments showed that the newly developed bionic corn test bench could achieve a high rate of ear picking. No grain damage was caused to the picked corn ears, so it was not recorded in the results analysis table. Additionally, the ear-picking test could be completed for corn plants with different growth directions and scion heights. This indicated the reasonable design of the test device, although additional field trials are recommended. Finally, the integrity of the corn straw could be ensured with less damage and breakage occurring after harvesting. This indicated that the design requirements for straw recovery could be satisfied by the test device. The ear-picking rates of each group in the tests are shown in

Table 4. Results of range analysis.

Test No.	Factors
	A (r/min)	B (m/s)	C (°)	yi (%)
1	(1)9	(1)1.0	(1)30	80.0
2	(1)9	(2)1.5	(2)40	92.5
3	(1)9	(3)2.0	(3)50	87.5
4	(2)11	(1)1.0	(2)40	77.5
5	(2)11	(2)1.5	(3)50	85.0
6	(2)11	(3)2.0	(1)30	85.0
7	(3)13	(1)1.0	(3)50	85.0
8	(3)13	(2)1.5	(1)30	97.5
9	(3)13	(3)2.0	(2)40	95
yj1	260.0	242.5	262.5	${\displaystyle \sum }_{\mathrm{i}=1}^9{\mathrm{y}}_{\mathrm{i}}=785$
yj2	247.5	275.0	265.0
yj3	280.0	267.5	257.5
${\overline{\mathrm{y}}}_{\mathrm{j}1}$	86.67	80.83	87.50
${\overline{\mathrm{y}}}_{\mathrm{j}2}$	82.50	91.67	88.33
${\overline{\mathrm{y}}}_{\mathrm{j}3}$	92.50	89.17	85.83
${\mathrm{R}}_{\mathrm{j}}$	10.00	10.84	2.50
Optimized level	A3	B2	C2
Primary and secondary factors	B, A, C
Optimal combination	A3 B2 C2

.

From the range analysis results, the picking rate was found to be affected most significantly by the corn-feeding speed, which was followed by the snapping roller speed. At the same time, it can also be impacted, to some degree, by the angle between the snapping rollers and the clamping conveyor, but these had a small effect compared with the first two test factors. The ear-picking rate can be improved by accelerating the feeding speed and snapping roller speed. However, when the feeding speed is too fast, it can easily cause a large downward bending effect of the snapping rollers on the ears of corn and an insufficient clamping force on the corn straw. As a result, the straw falls from the clamping device during the snapping process, which causes the entire plant to fall, thus ending the snapping process. Therefore, the range analysis was carried out based on these experimental phenomena. Obviously, the optimal factors for improving corn ear picking can be combined with a snapping roller speed of 780 r/min, a corn-feeding speed of 1.5 m/s, and an angle between the snapping roller and clamping conveyor of 40°.

Because the functional relationship between the ear-picking rate and the influencing factors needs to be further investigated, a fitting equation was conducted using the test results. The fitting equation was obtained as follows:

$$\widehat{y}=222.98-38.43A+1.77A_{}^2+81.45B-26.67B^2+0.62AB$$

(6)

Additionally, the variance analysis revealed the main influencing factors of the ear-picking rate y and the rotational speed of the snapping roller A, as well as the function between the corn feed speed B and the angle C between the snapping rollers and the holding device. To be specific, in the calculation process, the ear-picking rate was influenced less by C than it was the other two factors within the angle range in the ear-picking test, therefore, it can be ignored. From the equation, a nonlinear relationship can be found between the ear-picking rate and the snapping roller speed, as well as the corn-feeding rate [21], which are presented directly in the relationship obtained and shown in Figure 11.

5. Conclusions

A comparative test was conducted using two different mechanical methods for corn ear picking. When the average moisture content of corn straw was 75%, the average tensile fracture force applied for ear picking was 456.43 N, and the average bending fracture force was 51.86 N. When the average moisture content of the straw was 15%, the average tensile fracture force was 278.80 N for ear picking, and the average bending fracture force was 38.50 N. The results show that the bending fracture forces are much smaller than the tensile fracture forces required for the picking of corn in two different harvest periods.

A new bionic device for corn ear picking was designed based on the bending fracture principle. The utility of this device was proven by the test in this study, and it achieved corn ear picking with little damage occurring to the corn ears and straw. More importantly, ear picking could be accomplished successfully despite the corn having various growth directions and scion heights.

It was proven in the bench test that the ear-picking device was designed based on a sound principle and had a reasonable structure. An orthogonal test was performed on the factors that affected the ear picking. Based on the results, the corn-feeding and snapping roller speeds were found to have significant effects on the ear-picking rate. The optimal combination for ear picking is a rotational speed of the snapping rollers of 780 r/min, a corn-feeding speed of 1.5 m/s, and a 40° angle between the snapping rollers and clamping conveyor. Finally, the functional relationship between the influencing factors and the ear-picking rate was obtained.