Design and Testing of a Peanut Roller Digging Harvester

Abstract

In order to solve the problems that arise from poor fruit–soil separation, a high fruit burial rate, and a high crushing rate during peanut harvesting under clay-heavy soil conditions, a multistage roller peanut harvester that is suitable for operation in these environments was designed. Considering the growth conditions of peanuts and the agronomic requirements of planting, the movement process and separation operation mechanism of the seedling and fruit–soil were analyzed, coupled with the vibrating excavation device and the conveying roller group. A dynamic model of seedling fruit–soil coupled throwing and soil collisions on the conveyor roller was constructed. The structure and maximum swing angle of the vibrating excavation device, the number of stages of the conveying roller group, the diameter of the throwing roller, and other parameters were determined through analyses. Utilizing the design results, a prototype was built, and a multifactor test for the operation parameters was carried out. The forward speed of the machine, the excavation depth, and the speed of the conveyor roller were used as the test factors. The fruit burial rate and the peanut crushing rate were used as the test indexes. The Box–Behnken test method was used to establish a regression equation between the factors and the test indexes, and the influence law of each factor on the peanut harvest index was determined. When the optimal parameters were combined, i.e., 1.0 m/s, 150 mm, and 80 r/min, the fruit burial rate and crushing rate of peanuts were 6.2% and 6.4%, respectively. The performance of the machine meets the design requirements, and our research results can provide a reference for the research of mechanized peanut harvesting technology and equipment.

1. Introduction

Peanuts play a crucial role in global oil production and trade, ranking second only to soybeans, and are of vital significance in ensuring the security of the global edible oil supply [1,2]. According to the data released by the Food and Agriculture Organization of the United Nations (FAO), in 2022, the land for peanut farming in China amounted to 4.44 million hectares, accounting for 14.54% of the total worldwide area. In the same year, China’s peanut production reached 18 million tons, accounting for 33.21% of the total global production [3]. Nevertheless, compared with the mechanization level of peanut harvesting in the United States, Brazil, Argentina, and other countries, China’s mechanization level is relatively low. In 2021, the mechanized peanut harvest rate in China was only 65.65%, and a large number of peanut-growing areas still adopted mostly semi-mechanized and segmented harvesting methods, which had a severe impact on the development of the peanut industry [4,5].

Peanut harvesting methods can mostly be classified as combined harvesting, segmented harvesting, or two-stage harvesting methods [6]. The combined harvest method can sequentially complete a series of operations such as pulling up peanut plants, removing soil, picking fruit, cleaning, and centralized storage through a single piece of mechanical equipment [7]. The phased harvesting method involves various machinery and equipment to carry out the different steps of the peanut harvesting process. In two-stage harvesting, a peanut excavator is first utilized to conduct the initial harvest, complete the excavation, remove the soil, and lay it on the ground for drying; then, a peanut pickup and harvesting machine is employed to finish the subsequent work of picking and cleaning [8]. The application of the combined harvesting method in peanut harvesting is significantly influenced by soil properties like hardness and moisture content. At this stage, the harvest comprises fresh pods that have a high water content, which are more challenging to store; thus, combined harvesting methods are not suitable for large-scale peanut harvesting. The segmented harvesting technology, which does not require a high degree of mechanization, is more widely employed in countries with relatively limited technology, such as South and Southeast Asian countries like India, and African countries such as Nigeria. Peanut harvesting methods in the United States and other regions exhibit obvious two-stage harvesting characteristics, which have a long research history, a high level of mechanization, and remarkable efficiency. Such methods are highly suitable for large-scale peanut production and planting. Currently, China’s large-scale peanut-growing areas, such as Henan and Xinjiang, are also gradually introducing and applying this two-stage harvesting technology. The characteristics of peanut-producing areas in China (mainly upright growth) and those in the United States, Brazil, and other places (mainly vine varieties) are significantly different. In addition to the high cost of imported peanut harvesting equipment, the application of American-made harvesters in China’s peanut industry faces adaptability challenges.

At present, small peanut-digging harvesters are generally utilized in Chinese peanut harvesting. The excavator has a simple structure, and its main function is to dig peanuts out of the soil, but it does not effectively separate peanuts from the soil. After the excavation is completed, it is still necessary to manually shake the soil and pick up peanuts [9]. A sieve chain peanut harvester can simultaneously excavate peanuts and separate seedlings from the soil, and it spreads peanut plants in an orderly manner. However, its adaptability to sticky soil is poor, the separation of fruit and soil is difficult, and the buried fruit rate is high.

In recent years, some agricultural machinery research institutes, universities, and agricultural machinery manufacturing enterprises have carried out research work on peanut harvesting machinery. Currently, research on peanut harvesters mainly focuses on analysis to reduce the resistance of digging shovels and improve the fruit–soil separation mechanism. Hu Zhichao et al. [10] conducted an in-depth analysis of the stress of the peanut harvesting shovel and built a mechanical model of the shovel to simulate the digging state. Gao Lianxing’s team [11] invented a paired inclined excavation shovel, which effectively reduced the resistance in the excavation process by adjusting the angle of the shovel blade and the angle of slide cutting. Wang Dongwei et al. [12] carried out a simulation test analysis on the working performance of a wide-width digging shovel. Yang Ranbing et al. [13] designed a spring-toothed soil removal device and verified its effectiveness through soil removal mechanism analyses and field tests. Liu Zhixia et al. [14] optimized the parameters of key components of a chain vibration de-soil device with a toothed rod to improve its de-soiling efficiency. Although China started later than other countries in the research and development of peanut harvesting machinery, some progress has been made in recent years. Currently, the peanut harvesters developed in China are in a period of rapid development, especially peanut harvesters for sticky soil, but they still require further testing and exploration. Peanut harvesting machinery currently faces some challenges, such as high resistance during excavation and difficulty in effectively separating the fruit from the soil. In addition, the existing equipment in the process of harvesting is prone to burying fruit, and the pod damage rate is high. Therefore, there is an urgent need to develop a new peanut harvesting machine that can enhance soil removal efficiency and reduce harvest losses.

To solve the problem of heavy soil being difficult to break during the process of digging and harvesting peanuts, and considering that peanut pods are easily damaged, an innovative design scheme of a multistage roller peanut harvester is proposed in this paper. By deeply studying the dynamic process and separation mechanism of the fruit–soil bond in the vibration excavating device and the conveying roller set, a dynamic model of the throwing and crushing of clay mass on the conveying roller was established. Through an analysis of the design of the vibration mining device, the series of conveyor rolls, and the size of the throwing roller, the optimum working parameters were determined. The working parameters affecting the rate of burying and crushing of peanuts were determined, and multifactor tests were conducted. Field experiments verified the optimal working parameters of mechanical operation, which laid a foundation for the research of mechanization harvesting technology and equipment of the peanut industry.

2. Materials and Methods

2.1. Complete Machine Design and Working Principle

2.1.1. Peanut Plant Characteristics

At present, in the southern Henan Province, peanuts are mainly planted in ridges, with two rows in one ridge; a ridge height between 10 to 15 cm is used, with a sowing depth from 3 to 5 cm; and pods are concentrated in the range between 5 and 15 cm below the ridge surface [15]. The pod and vine are connected through the ovary stalk, and the peanut pods are distributed in a cone shape around the taproots in a spatial structure. Yuhua 37 in Zhumadian, Henan Province, was taken as the research object, and the triaxial size of the peanut plants at the appropriate harvest period was measured, as shown in Figure 1. Through data sampling and statistics, the average values of the measured radius, R, and depth, H, were found to be 5.31 cm and 15.52 cm, respectively.

2.1.2. Overall Structure

The multistage roller peanut harvester is pulled by a 604 tractor with a rear output shaft, which mainly consists of a digging vibration shovel, a seedling conveying device, a transmission system, and a frame. It can perform a series of operations such as peanut excavation, transportation, fruit–soil separation, orderly laying, etc. Its overall structure is shown in Figure 2.

The transmission system is composed of a gearbox, an output shaft, an eccentric wheel, a sprocket, a chain, etc. The spiral winch is distributed symmetrically in the front of the machine, which can realize the collection of peanut seedlings toward the middle. The excavating shovel is hinged to the front end of the bottom of the frame through the rocker arm and the pull rod. The device is composed of the shovel teeth and the grid rod, etc., and can loosen and break the soil under the action of the eccentric wheel. The pickup roller is located behind the digging shovel, and the peanut seedling–soil body enters the conveying roller through the digging shovel under the action of the pickup roller and the extrusion roller. The conveying roller is the key soil removal mechanism of the multistage roller peanut harvester. The conveying roller has four main stages, which are used to separate the excavated seedling–soil coupled body twice and continue to transport it back. The cleaned peanut seedlings are laid in an orderly manner by the spiral conveying roller. The main technical parameters of the multistage roller peanut harvester are shown in

Table 1. Main technical parameters.

Parameter	Value
Dimensions (L × W × H)/(mm × mm × mm)	1600 × 1650 × 980
Output power/(kW)	40–60
Rated speed/(r·min−1)	540
Working width/(mm)	1600
Digging depth/(mm)	0–250
Speed of operation/(km·h−1)	1.5–3.0
Productivity/(hm2·h−1)	0.25–0.45

.

2.1.3. Working Principle

During operation, the peanut harvester is driven by a tractor at a constant speed, and the vibration-digging shovel cuts the loose ridge body, digging up the peanuts along with the soil. The mixture of dirt and peanuts is pushed backward under the front end of the dirt and slides along the digging surface to the vibrating grid bar. Under the action of vibration, smaller soil blocks are screened, while some of the soil blocks are knocked so that they break under the action of the grid rod, and the broken soil blocks fall through the gap of the grid rod. Meanwhile, the unbroken soil blocks and peanut seedlings continue to move backward to the pickup roller. The peanut vine is forced to move backward into the conveyor roller under the action of the pickup roller rotation and of the suppression roller, and the peanut vine moves step by step on the conveyor roller to further break and remove the soil clods. Finally, under the action of the screw conveying roller, the peanut vine is concentrated to one side. Then, the complete excavation, conveying, soil removal, and orderly laying process is completed.

2.2. Design of the Key Components of Multistage Roller Peanut Digging and Harvesting Machine

2.2.1. Design of the Vibration Digging Shovel

The digging shovel is a core component of any peanut harvester. This component mainly realizes the important task of digging out the flower root fruit and soil clods from the ground. Its design and performance directly determine the working efficiency and harvest quality of a machine. As shown in Figure 3, the excavating shovel designed for this machine is composed of two parts: the shovel teeth and the grating rod. These are driven by CAM to carry out the vibration excavation.

In order to improve the excavation efficiency of the shovel and ensure the transmission and crushing function of the grid rods, it is necessary to ensure that the spacing between the grid rods can support the root fruit; accordingly, it is possible to effectively remove about 30% of the soil during the initial separation of the fruit–soil coupling while minimizing power consumption. According to the measured flower root fruit size, it is determined that the gap between adjacent grid rods should be less than 10.62 cm, so the gap is set at 10 cm. Dirt and peanut seedlings that are not broken in time will enter the pickup roll through the end of the grid rod, so the length and size of the grid rod should not be too small, ensuring the effective separation of soil and fruit.

Excessive impact causes damage to peanut pods, and the grid rod is prone to excessive bending. The test shows that the length of the grid rod is between 120 and 150 mm; the overall mass of the seedling soil forms bending torque on the grid rod under the action of gravity. The longer the grid rod, the greater the load mass and the greater the bending torque; the greater the deformation of the grid rod, the more likely it is to cause instability, thus affecting the operation effect. Through calculation, the length of the grid rod, L, is 150 mm; the structure of the vibrating excavating shovel is shown in Figure 4.

In order to ensure that the ground can be separated from the grid bar and the peanut seedlings can move along the grid bar axially, the eccentric rotation speed is between 220 and 330 r/min. The radial movement of peanut seedlings along the grid rod is the main cause of peanut pod breakage. In order to reduce pod breakage, the radial movement of the soil link of the seedlings on the grid rod should be controlled [16], and the critical condition for axial movement without radial movement is F_N ≥ 0; thus, the following can be obtained:

$$\left\{\begin{array}{l}{\mathrm{F}}_{\mathrm{A}}\mathrm{c}\mathrm{o}\mathrm{s}\mathsf{\theta }\gg {\mathrm{F}}_{\mathrm{f}}+\mathrm{G}\mathrm{s}\mathrm{i}\mathrm{n}\mathsf{\theta }\\ \mathrm{G}\mathrm{c}\mathrm{o}\mathrm{s}\mathsf{\theta }\gg {\mathrm{F}}_{\mathrm{A}}\mathrm{s}\mathrm{i}\mathrm{n}\mathsf{\theta }\end{array}\right.$$

(1)

In the formula, θ is the inclination angle of the grid bar, (°), and θ = 4°~10°.

$$\left\{\begin{array}{c}{\displaystyle \genfrac{}{}{0pt}{}{F_A=m_1{\omega }_1^2{S}_1\cos {\omega }_{1}t}{F_N=G\cos \theta -F_A\sin \theta }}\\ {\displaystyle \genfrac{}{}{0pt}{}{F_f=\tan \epsilon \left(G\cos \theta -F_A\sin \theta \right)}{{\omega }_1=n_1\pi /60}}\end{array}\right.$$

(2)

In the formula, m₁ is the mass of the seedling–soil coupled body, kg; S₁ is the grid rod amplitude, mm; t is the exercise duration, s; ε is the friction angle, (°), which is 30.5° by test; and n₁ is the rotation speed of the eccentric wheel when the seedling–soil coupled body moves along the axis, r/min.

$$\left\{\begin{array}{l}{n}_1\ge 30\sqrt{{\displaystyle \frac{g\tan (\epsilon +\theta )}{{\pi }^2{S}_1}}}\hfill \\ n_2\le {\displaystyle \frac{30}{\sqrt{S_1\tan \theta }}}\hfill \end{array}\right.$$

(3)

In the formula, n₂ is the rotation speed of the eccentric when the peanut seedling–soil coupled body moves along the grid bar axially without radial movement, r/min.

In order to operate correctly during excavation and harvest, the rotation speed range of the eccentric wheel is n₁ ≤ n ≤ n₂, and the amplitude of the grating rod is 122 mm < S₁ < 148 mm as determined through Equations (1) to (3). Through analysis, it can be seen that the larger the amplitude, the stronger the exciting effect; and the better the soil crushing effect, the better the shaking effect of the grid rod. Then, the amplitude is S₁ = 148 mm, and the eccentric rotation speed is n = 330 r/min. At the same time, the swing angle of the grid rod is

$$\alpha =2{\sin }^{-1}{\displaystyle \frac{S_1}{2L}}$$

(4)

In the formula, α is the swing angle of the grid rod, (°). The length of the grid rod L = 150 mm and the extreme value of the swing angle of the grid rod α = 59.12° can be obtained from Equation (4).

2.2.2. Design of the Conveying Roller Group

The conveying roller group consists of four groups of conveying rollers, as shown in Figure 5. The structure of a single conveying roller is mainly composed of a circular grid, a roller shaft, and a fixed disc. The conveyor roller is equipped with a sprocket at one end, and the sprocket is driven by a chain between two sprockets; the conveyor roller rotates in the same direction when it is working. The grid bar is evenly distributed along the circumference of the fixed disc; the roller is fixed between the plates on both sides of the frame through the bearing seat, and the conveyor rolls at all the levels are of the same height in the horizontal direction.

2.2.3. Conveyor Roll Spacing

The effect of soil breaking, sorting, and conveying in the process of groundnut digging and harvesting should be considered comprehensively. The distance between them is the minimum distance, S, between the outer circles of two adjacent conveying rollers. During operation, it is necessary to ensure that peanut seedlings do not fall from the gap, so the gap between the design conveying rollers should not be less than the minimum value of the triaxial size of the peanut seedlings, that is, S > 2R. At the same time, in order to satisfy the effect of soil crushing and soil removal, the spacing should be as large as possible on the premise of satisfying the transportation of seedlings, so the conveying roller gap is determined as S = 10 cm combined with the triaxial size of peanut seedlings.

2.2.4. Series of Conveyor Rolls

The peanut seedling–soil coupled body is forced into the conveying roller under the interaction of the pickup roller and the extrusion roller. During the process of being transported backward, the coupled body makes a parabolic movement and falls to the surface of the conveying roller after a certain height, Δh, is thrown, colliding with the roller body. In the process of throwing and colliding, the soil clods attached to the surface of peanut seedlings break and fall. As shown in Figure 6, the coupled peanut seedling and fruit–soil body is assumed to be a sphere for stress analysis, and its radius is r. The moment caused by the overturning and crushing of the joint body is mainly the moment caused by the collision between the joint body and the conveying roller. After n times of impact, the joint body will turn over and displace in the direction of the inertia moment, and the soil mass inside the joint body will produce a crushing displacement [17,18]; that is, the energy transfer of the inertia moment and the bonding moment inside the joint body will produce energy, so the energy equation of the soil mass attached to the surface of the rice is

$$\left\{\begin{array}{c}{E}_1=\mathrm{m}g\Delta h\\ E=m{r}^3{C}_1\end{array}\right.$$

(5)

where E₁ is the energy required for a single impact between the seedling–soil coupled body and the conveying roller, J; E is the total energy required for the crushing of the link of seedling soil, J; m is the mass of the seedling soil connector, kg; g is the acceleration of gravity, m/s²; Δh is the throwing height, mm; r is the radius of the coupled body, mm; and C is the bond strength, kPa.

Where the mass of the connection body is

$$m={\displaystyle \frac{4}{3}}\pi r^3{\rho }_b$$

(6)

In the equation is the capacity weight, g/cm³.

In order to break and separate the soil mass from the peanut seedling–soil coupled body, the collision frequency of the coupled body n can be expressed as

$${\mathrm{n}}_{\mathrm{c}}={\displaystyle \frac{E}{E_1}}$$

(7)

where n is the number of collisions required for the earth block to break away.

Combined vertical (5)~(7), can be obtained

$$n_{\mathrm{c}}={\displaystyle \frac{3C}{4{\rho }_{b}g\Delta h}}$$

(8)

The soil bulk density of the 150 to 250 mm soil layer was 1.5 to 1.7 g/cm³, which was determined as 1.7 g/cm³. Meanwhile, the soil moisture content was 18.6%, and the soil bond strength, C, was 9.6 kPa. Under the action of the conveying roller, the connected body of the seedling and soil makes a parabolic movement along the tangential direction of the conveying roller circumference and converts the kinetic energy generated by the collision into gravitational potential energy. According to the calculation of the energy conservation equation, the height of the parabolic movement ranges from 85 to 105 mm, and the throwing height was determined to be 95 mm. By substituting the parameters into Equation (8), n = 4.5 can be obtained, and the integer value is n_c = 4.0. According to the energy required for crushing the seedling–soil coupled body, the conveyor roll group is set as a four-stage roll group.

2.2.5. Conveying Roll Diameter

As shown in Figure 7, in the process of conveying the connected body by relay, the conveying roller forms an instantaneous collision force on the connected body. In order to crush the combined body, the impact force of the conveying roller on the connected body needs to be greater than the internal bonding force of the connected body. The moment equation is established with the center of the connected body as the coordinate origin, O:

$$\begin{array}{l}\left\{\begin{array}{c}{\mathrm{F}}_{\mathrm{n}1}{\mathrm{r}+\mathrm{F}}_{\mathrm{n}2}{\mathrm{L}}_{\mathrm{c}}{+\mathrm{G}}_1{\mathrm{L}}_{\mathrm{a}}{>\mathrm{F}}_{\mathrm{u}1}{\mathrm{L}}_{\mathrm{a}}\\ {\mathrm{F}}_{\mathrm{n}1}{\mathrm{r}+\mathrm{F}}_{\mathrm{n}1}{\mathrm{L}}_{\mathrm{d}}{+\mathrm{G}}_2{\mathrm{L}}_{\mathrm{b}}{>\mathrm{F}}_{\mathrm{u}2}{\mathrm{L}}_{\mathrm{b}}\end{array}\right.\end{array}$$

(9)

The internal binder of the seedling soil connector is

$$F_{u1}=F_{u2}=C{S}_u$$

(10)

L_a and L_b are the values of the horizontal distance between the centroid of the two soil blocks and point O after separation, in the unit of mm, L_a = L_b = 0.375r. L_c and L_d are the values of the vertical distance between the last two stages, throwing roller and O point, in mm. L_c = L_d = 0.5r; F_u1 and F_u2 are the values of the bond strength, in unit N; F_n1 and F_n2 are the values of the collision force of the conveying roller on the formation of the association, and the unit is N; G₁ and G₂ are the values of gravity exerted on the two soil blocks after separation, in unit N, G₁ = G₂ = mg; S_u is the value of the broken section area of the coupled body, in mm².

The gravity of the connection is

$$G_1=G_2=mg$$

(11)

When the conveying roller carries the seedling soil link back, the conveying roller grid will impact the link, and energy transfer will occur between the conveying roller and the link; the collision momentum and impulse can be expressed as

$$P_1=m_t{v}_t=F_n\Delta t$$

(12)

where P₁ is the collision momentum generated by the grid bar on the association, kg·m/s; F_n is the impact force of the grid bar on the association, N, and F_n = F_n1 = F_n2; Δt is the contact time of the two, s; ω_t is the angular speed of the conveyor roll, r/min; m_t is the mass of conveying roller, kg; and R is the radius of the conveyor roll, mm.

The soil block breaks and falls after the coupled body collides with the grid, and the grid collides with the peanut vine. At this time, the collision momentum and impulse of the conveying roller acting on the peanut vine can be expressed as

$$P_2={\mathrm{m}}_t{v}_t=F_p\Delta t$$

(13)

$${\mathrm{v}}_{\mathrm{t}}={\displaystyle \frac{\pi \mathrm{r}{n}_t}{30}}$$

(14)

where P₂ is the impact momentum of the conveying roller on the peanut, kg·m/s.

In order to achieve the effect of breaking the soil block of the connected body during transportation, the impulse generated by the impact should be greater than the bonding force inside the connected body; the impact damage to the peanut pod should be reduced; the impact force should be less than the damaging force, F_p, of the peanut pod. Combined with the damage impact force of the peanut pod = 10 N in the previous test, the joint vertical (6), (10)~(13) can be obtained

$${\displaystyle \frac{\Delta {\mathrm{t}(15\mathrm{r}}^2{\mathrm{C}}_1{-20\mathrm{r}}^3{\rho }_b\mathrm{g})}{{2\mathrm{n}}_{\mathrm{t}}{m}_t}}<R<{\displaystyle \frac{30F_p\Delta t}{\pi n_t{m}_t}}$$

(15)

Field data of peanuts during the optimum harvest period were ρ_b = 1.7 g/cm³, C₁ = 9.6 kPa, and g = 9.8 m/s². The preliminary test data are as follows: n_t = 60 r/min, m_t = 1.2 kg, Δt = 0.1 s, r = 120 mm, and F_p = 10 N. The relevant values were substituted into Equation (14) to obtain 143.6 mm > R > 132.7 mm, so the diameter of the conveying roller was determined as R = 135 mm.

2.3. Field Trial

2.3.1. Test Conditions

According to the structural design parameters of the whole machine, the 4HW-160 multistage roller peanut harvester was manufactured in the Engineering Research Center of Peanut farming, harvesting, and processing in Henan Province. In October 2023, the experiment was carried out in the peanut field of the modern agriculture Demonstration Park in Changyuan City, Henan Province. According to the depth of the peanut root and the range of peanut results, the soil firmness at a depth of 0 to 20 cm was measured. A five-point sampling method was adopted, and the average value of the measurement was measured three times at each point. Meanwhile, the soil moisture content was measured at each point. The measured soil bulk density was 1.7 g/cm³, the soil compactness was 9.6 kPa, and the water content was 18.6%. The peanut variety Yuhua 37 was planted in the experimental field, and two seeds were sown in one hole. The average maximum bearing radius was 6.52 mm, and the average maximum bearing depth was 16.35 mm. Plots with the same growth trend were selected for the test, and each group of tests was carried out over 5 m after the stable operation of the machine. Each group of tests was repeated three times to calculate the average peanut burying rate and peanut crushing rate. The field test of peanut harvest is shown in Figure 8.

2.3.2. Evaluation Index

The performance test of the multistage roller peanut harvester was carried out according to the industry standard NY/T 502-2016 Peanut harvester operation quality [19] “Operation Quality of the Peanut harvester”. The key technical indicators of the peanut harvester were peanut loss and peanut pod damage during the peanut harvesting process, and the peanut loss was mainly the rate of peanuts buried after the peanut pod was dropped and buried during the digging process. In practice, different working parameters were used to determine the buried rate of peanuts and the damage rate of peanut pods. The experiment selected the Yuhua 37 variety planted in a modern agricultural demonstration Park in Changyuan City, Henan Province. When the test data were collected, the unexcavated peanuts, the peanuts dropped during the excavation and transportation of soil, and the damaged peanuts were weighed and measured, respectively. Each group of tests was repeated three times, and the statistical results were averaged.

(1)

Peanut burying rate:

$$Y_1={\displaystyle \frac{W_2+W_3}{W_1+W_2+W_3}}\times 100\%$$

(16)

In the formula, Y₁ is the percentage of peanut buried fruit, %; W₁ is the total mass of peanuts actually harvested, kg; W₂ is the mass of unexcavated peanut, kg; and W₃ is the mass of peanuts dropped during the excavation and transportation of soil, including the mass of peanuts scattered on the surface and covered by soil clods, kg.

(2)

Peanut crushing rate:

$$Y_2={\displaystyle \frac{P_s}{W_1+W_2+W_3}}\times 100\%$$

(17)

In the formula, Y₂ is the peanut crushing rate, %; and P_s is the total mass of damaged peanuts (kg).

2.3.3. Test Scheme

In the process of groundnut excavation and laying, the advance speed of the machine, the depth of the digging shovel, and the speed of the conveying roller have significant effects on the damage and loss of groundnut pods. When the working speed of the machine is too fast, the digging depth is too deep, and the rotating speed is too large, the breakage rate of groundnut pods and the burying rate of groundnut pods increase significantly. In order to ensure working efficiency, the advancing speed of the machine should not be too low; the advancing speed of the machine should be between 0.5 and 1.0 m/s according to the actual work situation in the field. Considering the fruit-bearing characteristics of peanut pods, generally located at 120 to 150 mm underground, and considering other characteristics, such as the increase in digging resistance and soil feeding amount when the digging depth is too large, the excavation depth test value is 150 to 200 mm. When the conveying roller speed is too low, the crushing efficiency of the fruit–soil coupled body is reduced, resulting in backsoil. When the conveying roller speed is too high, the peanut pod is easily broken on impact. The suitable range of conveying roller speed is 70 to 110 r/min. In order to determine the optimal working parameters of the peanut harvester, optimization tests were carried out with the forward speed of the machine (A), the digging depth (B), and the conveyor roll speed (C) as the influencing factors. According to the parameter range determined by the pretest and the single-factor test, a Box–Behnken central combination test was used to carry out a three-factor, three-level orthogonal test [20,21]. A test factor coding table is shown in

Table 2. Coding table of test factors.

Level	A/(m∙s−1)	B/mm	C/(r∙min−1)
−1	0.5	150	70
0	0.75	175	90
+1	1.0	200	110

.

2.3.4. Test Results

Field trials of mechanized peanut harvesting were carried out according to the experimental design, and the experimental data were collected according to the experimental scheme. The orthogonal experimental scheme and experimental data are shown in

Table 3. Experimental data.

Serial Number	A/(m∙s−1)	B/(mm)	C/(r∙min−1)	Embedded Fruit Rate, Y1/%	Percentage of Breakage, Y2/%
1	0.75	200	110	21.5	18.5
2	0.75	175	90	7.6	10.6
3	0.75	175	90	4.3	10.8
4	0.5	150	90	4.7	9.6
5	0.75	200	70	25.1	3.9
6	0.75	150	70	14.6	5.2
7	0.5	200	90	10.6	14.2
8	1	175	70	15.6	4.6
9	0.75	175	90	8.2	9.8
10	1	150	90	3.7	13.9
11	0.75	175	90	9.3	11.1
12	0.5	175	70	15.2	4.7
13	0.5	175	110	19.4	23.2
14	1	175	110	17.3	20.9
15	1	200	90	13.8	8.7
16	0.75	175	90	7.8	10.6
17	0.75	150	110	17.8	20.7

.

2.3.5. Analysis of Experimental Results

Design-Expert12.0 software (Version:13.0.5.0 64-bit) was used to analyze the variation in peanut burying rate and peanut crushing rate. Detailed results are shown in

Table 4. Analysis of variance of the regression equation.

Source	Embedded Fruit Rate, Y1/%
	Sum of Squares	df	Mean Square	f-Value	p-Value
Model	623.20	9	69.24	22.74	0.0002
A-A	0.0313	1	0.0313	0.0103	0.9222
B-B	114.01	1	114.01	37.43	0.0005
C-C	3.78	1	3.78	1.24	0.3020
AB	4.41	1	4.41	1.45	0.2680
AC	1.56	1	1.56	0.5130	0.4970
BC	11.56	1	11.56	3.80	0.0924
A2	4.71	1	4.71	1.55	0.2537
B2	13.91	1	13.91	4.57	0.0699
C2	463.55	1	463.55	152.20	<0.0001
Residual	21.32	7	3.05
Lack of Fit	7.27	3	2.42	0.6896	0.6042
Pure Error	14.05	4	3.51
Source	Percentage of breakage, Y2/%
	Sum of squares	df	Mean square	f-Value	p-Value
Model	573.15	9	63.68	90.60	<0.0001
A-A	1.62	1	1.62	2.30	0.1728
B-B	2.10	1	2.10	2.99	0.1274
C-C	526.50	1	526.50	749.01	<0.0001
AB	24.01	1	24.01	34.16	0.0006
AC	1.21	1	1.21	1.72	0.2309
BC	0.2025	1	0.2025	0.2881	0.6081
A2	5.54	1	5.54	7.89	0.0262
B2	0.0684	1	0.0684	0.0974	0.7641
C2	11.08	1	11.08	15.77	0.0054
Residual	4.92	7	0.7029
Lack of Fit	3.99	3	1.33	5.74	0.0623
Error	0.9280	4	0.2320

. Regression models were constructed for peanut burying rate, Y₁, and peanut crushing rate, Y₂, respectively. The p-value test results show that the peanut burying rate was significantly affected by the digging depth (B), while the peanut crushing rate was significantly affected by the conveyor roller speed (C). Accordingly, the effects of various factors on peanut burying rate, Y₁, and peanut crushing rate, Y₂, can be expressed by their respective regression equations.

$$\left\{\begin{array}{l}\begin{array}{l}{Y}_1=7.44+0.063A+3.78B+0.69C+1.05AB\\ -0.63AC-1.70BC-1.06A^2+1.82B^2+10.49C^2\end{array}\hfill \\ \begin{array}{l}{Y}_2=10.58-0.45A-0.51B+8.11C-2.45AB\\ -0.55AC-0.23BC+1.15A^2-0.13B^2+1.62C^2\end{array}\hfill \end{array}\right.$$

(18)

The test results were processed through difference analysis in the Design-Expert12.0 software, as detailed in Table 4. In the variance analysis of the peanut embedding rate, the p-value of the missing fitting term was 0.08, which exceeded the significance level of 0.05. As shown in the analysis of the peanut crushing rate, the p-value of the missing fitting term is 0.016, which is also higher than the significance level of 0.01. This indicates that the p-values of the missing items of the two indexes are not significant, which confirms that the regression equation has a high degree of fitting to the peanut embedding rate and peanut crushing rate and further indicates that no other key factors have a significant impact on the test results.

3. Results and Discussion

3.1. Response Surface Analysis

In order to more intuitively analyze the influence of various interacting factors on the embedding rate and pod damage rate of peanuts, a response surface diagram was drawn using Design-Expert12, as shown in Figure 9.

The response surface of the digging depth and conveying roller speed to the buried fruit rate when the forward speed is 0.75 m/s is shown in Figure 9a. When the front feed speed is constant, the embedding rate decreases with the increase in the conveyor roller speed. When the speed increases to 90 r/min, the embedding rate is the smallest; then, it increases with the increase in the rotating speed. The rate of buried fruit increased with the increase in digging depth.

The response surface of the forward speed and the conveyor roller speed to the buried fruit rate when the digging depth is 175 mm is shown in Figure 9b. When the digging depth is constant, the buried fruit rate decreases with the increase in the conveyor roller speed. When the roller speed increases to 90 r/min, the buried fruit rate is the smallest; then, it increases with the increase in the rotating speed. The embedding rate of fruit increased slowly with the increase in advance speed.

When the conveyor roller speed is 90 r/min, the response surface of forward speed and digging depth to the buried fruit rate is shown in Figure 9c. When the conveyor roller speed is constant, the rate of buried fruit increases with the increase in digging depth. The embedding rate increased with the increase in advance speed but had little effect on the overall embedding rate.

When the conveyor roll speed is 70 r/min, the response surface of forward speed and digging depth to the crushing rate is shown in Figure 9d. When the conveyor roller speed is constant, the crushing rate increases with the increase in the forward speed. The crushing rate exhibits no clear trend with the increase in digging depth.

3.2. Model Optimization and Experimental Verification

Aiming for the lowest crushing rate and embedding rate, the regression equation was solved with the help of the optimization module in the Design-Expert12.0 software to obtain the best results. The set of conditional equations for objectives and constraints was as follows:

$$\left\{\begin{array}{c}\min Y_1(A,B,C_3)\\ \min Y_2(A,B,C)\\ 0.5\le A\le 1.0\\ 150\le B\le 200\\ 70\le C\le 110\end{array}\right.$$

(19)

An optimal analysis of each parameter was performed in the Design-Expert12.0 software, aiming to find the best combination of working parameters. After the peanut harvester was improved, its travel speed was set to 1.0 m/s, the digging depth was adjusted to 150 mm, and the speed of the conveyor roller was set to 79.11 r/min. Under these parameters, the buried peanut rate was 6.19%, and the broken peanut rate was 6.41%. After adjustment, the traveling speed of the peanut harvester was fixed at 1.0 m/s, and the depth of its digging operation was 150 mm. At the same time, the rotation speed of the conveyor drum was set to 80 r/min. In field experiments, the rate of buried peanuts in soil was 6.2%, and the rate of breakage during harvest was 6.4%.

3.3. Comparative Test Under Optimized Conditions

As shown in Figure 10a comparison test of the 4HW-160 multi-roll peanut harvester, the 4H-160 chain screen peanut harvester, and a vibrating-screen peanut harvester was carried out in the field. A peanut field with clay-heavy soil was selected for the test site, and a series of standard operating parameters were set to ensure that other relevant conditions were consistent in the test performance evaluation of the machine. The specific working parameters included the following: the travel speed was set to 1.0 m/s, the digging depth was set to 150 mm, and the speed of the throwing roller was set to 80 r/min. The actual measurement data of operation effect evaluation indexes corresponding to different harvesting techniques were obtained through experiments; these data are presented in

Table 5. Measured values of each evaluation index under optimization conditions.

Harvesting Method	Embedded Fruit Rate/%	Percentage of Breakage/%	Total Loss Rate/%
4HW-160 multi-roll peanut harvester	6.5	7.3	13.8
4H-160 chain rod peanut harvester	11.4	5.2	16.6
4H-160 vibrating-screen peanut harvester	13.8	9.1	22.9

.

According to the data in Table 5, the actual measurement results of the 4HW-160 model multistage roller peanut harvester in terms of the peanut burying rate are 3.9% and 7.3% lower than the other two models, respectively. This result shows that the model has better soil-breaking performance than the other two models in the viscous soil environment. In the comparative test, the effect of the 4HW-160 multistage roller peanut harvester is clear: its total operating loss rate was reduced by 2.8% and 9.1% compared with the other two models. The experiment shows that the machine has a better operation effect than the traditional peanut harvester in viscous soil.

4. Conclusions

The developed 4HW-160 vibrating peanut harvester has the characteristics of high efficiency and multiple functions. The machine includes key components, such as a vibrating excavating device and a conveying roller, which can complete a series of processes, such as digging, removing soil, conveying, and laying peanuts simultaneously.

The motion model of the vibration mining device was constructed, and the interaction between the structure size of the conveyor roller and its working parameters was determined. A kinematic model of soil clods and peanuts on the conveyor roller was established to ensure the effect of soil crushing and effectively reduce the damage to peanuts. The diameter of the conveyor roller was determined to be 250 mm using conveyor stage 4.

After a multifactor test and the optimization test verification, the best operating parameters were established for the 4HW-160 model vibrating-screen peanut picker: a traveling speed of 1.0 m/s, a digging depth of 150 mm, and a conveyor roll speed of 80 r/min. After field verification, the optimized operation effects of the machine were 6.5% and 7.3%, which meet the operation standards for peanut harvesting.