Design and Experiment of a Dual-Disc Potato Pickup and Harvesting Device

Abstract

To address the inefficiency and high cost of manual potato pickup in segmented harvesting, a dual-disc potato pickup and harvesting device was designed. The device utilizes counter-rotating dual discs to gather and preliminarily lift the potato–soil mixture, and combines it with an elevator chain to achieve potato–soil separation and transportation. Based on Hertz’s collision theory, the impact of disc rotational speed on potato damage was analyzed, establishing a maximum speed limit (≤62.56 r/min). Through kinematic analysis, the disc inclination angle (12–24°) and operational parameters were optimized. Through coupled EDEM-RecurDyn simulations and Box–Behnken experimental design, the optimal parameter combination was determined with the potato loss rate and potato damage rate as evaluation indices: disc rotational speed of 50 r/min, disc inclination angle of 16°, and machine forward speed of 0.6 m/s. Field validation tests revealed that the potato loss rate and potato damage rate were 1.53% and 2.45%, respectively, meeting the requirements of the DB64/T 1795-2021 standard. The research findings demonstrate that this device can efficiently replace manual potato picking, providing a reliable solution for the mechanized harvesting of potatoes.

1. Introduction

Mechanized potato harvesting generally employs two approaches: combined harvesting and segmented harvesting. Most developed countries in Europe and America predominantly utilize combined harvesting, which can accomplish multiple operations such as potato digging, lifting, soil separation, impurity removal, and loading/unloading in a single pass. However, this method typically results in a higher potato damage rate and is generally employed for starch potatoes and potatoes intended for deep processing. In China, the primary use of potatoes and their derivatives is for direct consumption, with the proportion of fresh potatoes continuously increasing. To minimize potato damage, the majority of potato-producing regions in China predominantly adopt segmented harvesting, which represents a semi-mechanized approach. Segmented harvesting involves a multi-step process: first, the potato vines are eliminated using a vine killer machine; subsequently, a potato digging and harvesting machine is employed to perform tasks such as tuber excavation, soil separation, and row placement of the potatoes. Finally, the potatoes are manually collected and bagged [1,2,3,4,5,6]. Potato skin toughness increased significantly after drying. Manual collection effectively reduces damage during the harvesting process, thereby mitigating associated economic losses. However, the inefficiency and high labour costs of manual collection severely hinder the development of the potato industry and the progression of fully mechanized potato harvesting. As a result, the development of a potato pickup and harvesting machine has become an inevitable trend.

At present, the domestic potato pickup harvester is in its infancy, mostly using an excavation harvester for secondary excavation of potatoes, instead of the picking process. Xiaoli, Yan [7], and others developed a shovel-type small potato picker that can complete potato picking, potato soil separation, ascending and transporting, and other operations, with the adaptability of small plots and a lower rate of injury to potatoes. Kailiang, Lu [8], and others developed a finger-type potato pickup device, which can initially complete the potato pickup and the potato soil separation process, and the design of the deflector roller effectively solved the congestion problem of the traditional shovel structure. Xiaoyu and Fan [9] designed an elastic tooth potato pickup and harvesting device, which utilizes elastic teeth to complete the potato pickup operation at a small depth of entry. Currently, on the market, most of the potato pickup harvesters, due to the complex structure or injury rate, leakage rate, and other key indicators, cannot be universally promoted and applied due to the difficulty of meeting market requirements.

This paper designs a dual-disc potato pickup and harvesting device, analyzes the kinematics of the disc pickup process, derives the structural parameters and working parameters of the pickup device, adopts the method of EDEM-RecurDyn coupling to simulate and analyze the working process of the device, obtains the optimal combination of the working parameters of the machine, and carries out a verification of the field test. The device can replace manual potato picking operations, improve the potato picking and harvesting efficiency, and ensure a lower rate of injury and leakage.

2. Overall Structure and Working Principle of the Picking Device

2.1. Overall Machine Structure

The dual-disc potato pickup harvesting device is mainly composed of a pickup disc, transmission box, ascending and transporting chain device, frame, ground wheel, and other devices; the structure is shown in Figure 1.

2.2. Working Principle of the Pickup Device

The field for potato pickup operations is prepared by a potato digger, which leaves the soil relatively loose after excavation. The harvested potatoes are then evenly distributed on potato ridges of generally consistent height [10]. During operation, the dual-disc potato pickup harvesting device features two sets of pickup discs at the front end, which are angled relative to the ground surface. These discs rotate in opposite directions to gather and initially lift the mixture of soil and potatoes. The pickup discs are separated by a certain gap, allowing for the initial separation of soil and impurities. Driven by soil resistance and the action of the discs, the mixture of soil and potatoes is conveyed into the rear elevator chain for further screening of soil and debris. The cleaned potatoes are then transported by the elevator chain to the rear lifting device.

3. Design of Key Components

3.1. Design of Pickup Disc Dimensions

In the context of segmented potato harvesting, the primary operation involves the excavation and collection of potatoes. Once excavated, the potatoes are laid out in a relatively regular strip pattern for field drying. The physical parameters of the potatoes, which are relevant to the design of the potato pickup device, mainly include the distribution width, physical dimensions, and mass of the potatoes. For instance, random sampling of the physical parameters of the Xisen No. 6 potato variety during the harvesting period is summarized in

Table 1. Physical parameters of potatoes during harvesting period.

Item	Parameter
Distribution Range Width of Potato (mm)	300~550
Length of Single Potato (mm)	80~120
Width of Single Potato (mm)	46~75
Height of Single Potato (mm)	41~56
Mass of Potato (g)	120~310

.

Based on the distribution width of potatoes on the ground after digging and the physical dimensions of the potatoes, the operating width of the potato pickup device was designed to be 800 mm. Consequently, the diameter d of a single pickup disc was set at 400 mm, and the maximum spacing d1 between the disc bars was designed to be 35 mm. The structure of the pickup disc is illustrated in Figure 2, with 65Mn steel selected as the material for the pickup disc.

3.2. Design of the Pickup Disc Angle

After being dug up by the potato harvester, the soil becomes loosened, and potatoes are distributed on the surface in various patterns. The potatoes exposed on the ground, mingled with clods and roots, are referred to as “visible potatoes”, while those entirely or partially covered by soil are termed “hidden potatoes”. Following the excavation, potatoes are distributed either on the surface or at a depth ranging from 30 to 50 mm below the surface [11].

The pickup disc should be designed to collect all potatoes, including both visible and hidden ones, to avoid missed pickups. Simultaneously, it should prevent excessive soil penetration, which could lead to soil accumulation and clogging. Based on the distribution state and height of potatoes after excavation, the penetration depth of the pickup shovel should be controlled within the range of 50–100 mm and should be adjustable to accommodate varying conditions.

During the operation of the pickup disc, the forces acting on the potato are illustrated in Figure 3. Based on the force analysis, the following relational equation can be established:

$$\left\{\begin{array}{l}P\cos \alpha -T-G\sin \alpha =0\\ R-G\cos \alpha -P\sin \alpha =0\\ T=\mu R\end{array}\right.$$

(1)

In the formula, P represents the force required for the potato to move along the pickup disc, measured in Newtons (N); R denotes the supporting force exerted by the pickup disc on the potato, also in Newtons (N); G signifies the gravitational force acting on the potato, measured in Newtons (N); α is the inclination angle of the pickup disc, in degrees (°); T stands for the frictional force experienced by the potato, measured in Newtons (N); and μ indicates the coefficient of friction.

From the aforementioned formula (1), the calculation formula for the inclination angle α of the pickup disc can be derived as follows:

$$\alpha =arctg{\displaystyle \frac{P-\mu G}{\mu P+G}}$$

(2)

The friction coefficient between the pickup disc and the soil ranges from 0.5 to 0.75, and the soil density is ρ = 1380 kg/m³. As indicated by Equation (2), the greater the inclination angle of the pickup disc, the larger the operational resistance it experiences. Based on the theoretical and empirical studies of potato digging and harvesting [12], the optimal penetration angle for a digging blade is generally between 20° and 30° for maximum efficiency. According to the anticipated functional requirements of the pickup device, the pickup discs penetrate the soil at a shallow depth, and the demand for soil fragmentation rate is relatively low. By integrating Equations (1) and (2), the optimal inclination angle for the pickup blade is determined to be between 12° and 24°. This range ensures the smooth pickup of potatoes while minimizing the rate of tuber damage. Additionally, it avoids issues such as increased pickup resistance caused by excessive inclination angles.

3.3. Selection of Pickup Disc Rotation Speed

During the picking process, collisions between the disc grid bars and potatoes are the primary cause of potato damage. When potatoes come into contact with the grid bars, collisions occur at a certain relative velocity, and the extent of damage is closely related to the intensity of the collision. To identify the factors influencing potato damage, Hertzian collision theory [13,14] is employed to analyze the main factors affecting the magnitude of contact stress during collisions.

When a collision occurs, the duration of action is brief, and the contact area is extremely small. To simplify the analysis, the contact collision between the potato and the grid bar is equated to a collision between two spheres. Based on Hertzian contact theory, the following assumptions are proposed:

(1)

The potato is simplified as a homogeneous and isotropic ellipsoid.

(2)

The contact area is very small, and the contact is non-conformal. Near the initial contact point, both the potato and the disc grid bar can be regarded as elastic half-spaces.

(3)

During the contact process, the deformation of the potato is much smaller than its size. Near the initial contact point, the surfaces of the potato and the grid bar contact at points intersecting with the normal of the tangent plane at the initial contact point.

(4)

The rotational motion during the collision and the friction during contact are neglected, so the tangential internal forces are zero.

(5)

The surfaces of the potato and the grid bar near the initial contact point are second-order continuous, and the contact area is elliptical, with “a” as the major axis and “b” as the minor axis.

The collision of the potato with the fence pole is shown in Figure 4. According to Hertz contact theory, when two objects of general shape come into contact, the size of the contact area c, the compression δ, and the maximum contact stress P on the contact surface are, respectively, given by

$$\left\{\begin{array}{l}c=(ab{)}^{{\displaystyle \frac{1}{2}}}={\left({\displaystyle \frac{3F{R}_e}{4E_d}}\right)}^{{\displaystyle \frac{1}{3}}}\\ \delta ={\left({\displaystyle \frac{9F^2}{16{E_d}^2{R}_d}}\right)}^{{\displaystyle \frac{1}{3}}}{F}_2\left(e\right)\\ P={\displaystyle \frac{3F}{2\pi ab}}={\left({\displaystyle \frac{6F{E_d}^2}{{\pi }^3{R_d}^2}}\right)}^{{\displaystyle \frac{1}{3}}}{\left\{F_2\left(e\right)\right\}}^{-{\displaystyle \frac{2}{3}}}\end{array}\right.$$

(3)

Based on this, the collision contact stress P and the collision contact force F experienced by the potato block when it collides with the grid bar can be determined as follows:

$$\left\{\begin{array}{c}P={\displaystyle \frac{2}{\pi }}{E}_d{\left({\displaystyle \frac{\delta }{R_d}}\right)}^{{\displaystyle \frac{1}{2}}}\\ F={\displaystyle \frac{4}{3}}{E}_d{R}_d^{{\displaystyle \frac{1}{2}}}{\delta }^{{\displaystyle \frac{3}{2}}}\end{array}\right.$$

(4)

In the formula, E_d represents the equivalent elastic modulus of the potato block and the grid bar in MPa, R denotes the equivalent radius of the contact area between the potato block and the grid bar in mm, and F₂(e) is the correction factor.

Here, F denotes the collision contact force between the potato and the grid bar in N; δ represents the deformation of the potato in mm; R₁ is the radius of curvature in the contact area between the potato block and the grid bar in mm; R₂ indicates the radius of the grid bar in mm; R_d is the equivalent radius of the contact area between the potato block and the grid bar in mm; and V_d signifies the instantaneous relative velocity during the collision between the potato and the grid bar in m/s.

As indicated by Equation (4), the deformation of the potato block’s contact surface is directly proportional to the applied load. The potato, being an elastoplastic material, initially undergoes elastic deformation upon collision. Damage begins to occur when the collision-induced stress on the potato reaches the yield stress [15].

Based on the given assumptions, when two spheres with radii R₁ and R₂ collide with each other, the equivalent radius Rd and the equivalent elastic modulus can be expressed as

$$\left\{\begin{array}{l}{R}_d={\displaystyle \frac{1}{R_1}}+{\displaystyle \frac{1}{R_2}}\\ {\displaystyle \frac{1}{E_d}}={\displaystyle \frac{1-{{\mu }_1}^2}{E_1}}+{\displaystyle \frac{1-{{\mu }_2}^2}{E_2}}\end{array}\right.$$

(5)

In the formula, E₁ represents the elastic modulus of the potato block in MPa, μ₁ denotes the Poisson’s ratio of the potato block, E₂ signifies the elastic modulus of the grid bar in MPa, and μ₂ represents the Poisson’s ratio of the grid.

According to Newton’s second law, we can derive

$${\displaystyle \frac{d{v}_t}{dt}}={\displaystyle \frac{d^2{\delta }_t}{d{t}^2}}$$

(6)

In the formula, v_t represents the collision velocity between the potato block and the grid bar at time t, in units of mm/s, and δ_t denotes the deformation of the contact surface at time t, in units of mm.

From Equation (6), the collision velocity between the potato block and the grid bar after time t can be derived as

$$v_t={\displaystyle \frac{d{\delta }_t}{dt}}$$

(7)

The process from the initial contact of the potato block with the grid bar to its departure post-collision adheres to the law of conservation of energy.

$$\left\{\begin{array}{l}{\displaystyle \frac{1}{2}}m{v_d}^2-{\displaystyle \frac{1}{2}}m{\left({\displaystyle \frac{d{\delta }_t}{dt}}\right)}^2=U\\ {\displaystyle \frac{1}{m}}={\displaystyle \frac{1}{m_1}}+{\displaystyle \frac{1}{m_2}}\end{array}\right.$$

(8)

In the equation, U represents the potential energy generated from the elastic deformation after the collision between the potato block and the grid bar, in Joules (J); and m denotes the equivalent mass of the potato block and the grid bar, in kilograms (kg).

$$F={\displaystyle \frac{\partial U}{\partial \delta }}$$

(9)

By combining Equation (4) and Equation (9), the elastic potential energy during the collision process can be derived.

$$U={\displaystyle \frac{8}{15}}{E}_d{\left(R_1{R}_2\right)}^{{\displaystyle \frac{1}{4}}}{\delta }^{{\displaystyle \frac{5}{2}}}$$

(10)

When the collision velocity of the potato block decreases to 0, the elastic potential energy of the collision reaches its maximum, and the deformation of the potato block is also at its maximum. By substituting Equation (10) into Equation (8), the maximum deformation δ_max of the potato block after collision with the grid bar can be calculated as follows:

$${\delta }_{\max }={\left({\displaystyle \frac{15m_1{m}_2{V_d}^2}{16E_d\left(m_1+m_2\right){R_d}^{\frac{1}{2}}}}\right)}^{{\displaystyle \frac{2}{5}}}$$

(11)

By substituting Equation (8) into Equation (1), the maximum contact stress P_max exerted on the potato block can be obtained as follows:

$$P_{\max }={\displaystyle \frac{2}{\pi }}{\left({\displaystyle \frac{E_d}{{R_d}^{\frac{3}{4}}}}\right)}^{{\displaystyle \frac{4}{5}}}{\left({\displaystyle \frac{15m_1{m}_2{V_d}^2}{16\left(m_1+m_2\right)}}\right)}^{{\displaystyle \frac{1}{5}}}$$

(12)

Analysis reveals that the maximum contact stress and deformation sustained by potato tubers during their collision with grid bars are primarily related to the bars’ elastic modulus, radius, and the instantaneous velocity of the collision. The maximum contact stress exerted on potato tubers during collision with grid bars is directly proportional to the elastic modulus of the bars. Therefore, selecting materials with a lower elastic modulus for the grid bars can effectively reduce the maximum contact force experienced by the tubers. Additionally, under constant conditions, a larger grid bar radius leads to a smaller maximum contact force on the potato tubers during collision [16].

According to Reference [17], the critical height for initial damage during collision between potato tubers and colliding objects increases with rising temperature. At 15 °C, the critical height for severe skin breakage in potato tubers colliding with 65Mn steel is 350 mm. Based on the law of energy conservation,

$$mgh={\displaystyle \frac{1}{2}}m{v}^2$$

(13)

In the equation, v is the instantaneous relative velocity at the moment of impact, m/s; h is the drop height of the potato, m; and m is the mass of the potato, kg.

Through calculation, the critical velocity at which damage occurs in the collision between the potato and the grid bar is

$$v_{\max }=2.62 \mathrm{m}/\mathrm{s}$$

(14)

The disc undergoes uniform circular motion, and the relationship between its tangential velocity at the endpoint and rotational speed is

$$V_{d\max }=2\pi nR$$

(15)

Here, V_b represents the tangential velocity at the endpoint of the disc (m/s); n denotes the rotational speed of the disc (r/s); and R is the radius of the disc (m).

This leads to the formula for calculating the rotational speed of the disc as

$$n_{\max }={\displaystyle \frac{V_{d\max }}{2\pi R}=62.56 \mathrm{r}/\min }$$

(16)

Therefore, the maximum speed of the pick-up disc should not exceed 62.56 r/min.

The dual-disc potato pickup and harvesting device, as an integral part of the main unit, should coordinate with the system to complete tasks including potato pickup and feeding, soil–potato separation, primary conveying, and subsequent elevation. During operation, the disc inclination angle, disc rotational speed, and machine forward speed are critical indicators affecting both the operational efficiency of the pickup device and the potato damage rate. Drawing from the theoretical and empirical foundations of potato harvesting, the soil-entry angle for digging shovels in ridge-based potato harvesting is typically set to 20–30°. Based on actual operational conditions during potato pickup and a comprehensive consideration of pickup performance and structural integrity, the soil-entry angle of the pickup disc is determined to be 12–18°, with a disc radius of 400 mm. Through analysis of the collision process between potatoes and grid rods, the theoretical maximum rotational speed that avoids potato damage was determined. As rotational speed increases, the relative collision velocity increases, leading to greater contact stress on the potatoes. To minimize damage while maintaining harvesting efficiency, the maximum rotational speed of the disc should be kept below the critical damage threshold. The recommended range for disc speed was set at 45–55 rpm, which was further validated through simulation tests and field trials. Additionally, integrated with practical experience in potato harvesting operations, the recommended forward speed of the entire machine ranges from 0.5 to 0.7 m/s.

4. Simulation Analysis

To determine the optimal operational parameters for the dual-disc potato pickup device, test models of the pickup device and soil ridge were constructed using discrete element software and multibody dynamics software [18,19,20], and discrete element simulation tests were conducted on the pickup device.

4.1. Development of Discrete Element Method Simulation Model

4.1.1. Potato Model Construction

To acquire relatively accurate potato shape parameters, three potatoes of different shapes with masses close to the overall sample average of harvested potatoes were selected. Three-dimensional scanning technology was employed to establish three-dimensional mesh models of these potatoes. The models in STL format were imported into EDEM 2022 software, and subsequently, potato discrete element models were obtained through the granule auto-filling method, as shown in Figure 5.

4.1.2. Soil Particle Model Construction

In potato pickup operations, the soil post-excavation is loose with minimal large clods and no compaction or adhesion. To ensure simulation accuracy while maintaining computational efficiency, soil particles were modelled at a size of approximately 5 mm; three differently shaped particles were selected to simulate the actual shapes of soil particles as illustrated in Figure 6.

4.1.3. Soil Ridge Model Construction

Based on field measurements of actual working plots post-potato excavation and spreading, a soil bin model was established (Figure 7). The soil ridge measured 4 m in length, 1 m in base width, and 0.2 m in height. Potatoes were randomly distributed across the soil ridge surface within a width of approximately 0.5 m.

The discrete element simulation parameters [21] are detailed in

Table 2. Basic parameters.

Item	Soil	Potato	Steel
Density (kg/m3)	1380	1184	7800
Poisson’s ratio	0.2	0.28	0.42
Shear modulus (Pa)	9 × 107	2 × 106	7.9 × 1010

and

Table 3. Interaction parameters.

Item	Collision Recovery Coefficients	Coefficient of Static Friction	Coefficient of Rolling Friction
Soil–soil	0.15	0.56	0.19
Potato–potato	0.66	0.48	0.02
Soil–potato	0.53	0.45	0.01
Potato–steel	0.45	0.44	0.27
Soil–steel	0.17	0.40	0.30

. The Hertz–Mindlin with JKR contact model was adopted to characterize interactions between potatoes and soil particles.

4.1.4. Simulation Process

The 3D model of the pickup device equipped with a reverse chain, created in SolidWorks 2023, underwent lightweight processing and was exported in .xt format for import into RecurDyn 2023 software. Constraints, contacts, and motion parameters were applied in RecurDyn 2023, after which the.wall file was exported and imported into EDEM 2022. The simulation time step was set to 0.01 s, and co-simulation was performed as illustrated in Figure 8.

Based on References [22,23,24,25] and the empirical test results, potatoes are deemed bruised when their maximum contact force during collisions reaches or exceeds 150 N, which may cause epidermal or tissue damage. Force analysis on potatoes was conducted in EDEM 2022. The parameters were as follows: disc rotation speed: 55 rpm; disc inclination angle: 16°; and machine forward speed: 0.6 m/s. The force profile of a potato at 3.2 s simulation time is shown in Figure 9. The results indicate that the contact force significantly increases to 150 N when the potato disengages from the pickup disc and interacts with the elevator chain.

4.2. Test Indicators and Measurement Methods

As the core component of the potato pickup harvester, the performance of the pickup device directly affects the overall operational efficiency. In accordance with the specifications of DB64/T 1795-2021 “Technical Specification for Mechanical Potato Pickup Operations” [26], the missed potato rate and bruised potato rate were selected as key evaluation indicators for the performance of the finger-type potato pickup device.

(1)

Missed Potato Rate

After the pickup device completed its operation, the successfully picked potatoes and missed potatoes were separately collected and weighed. The missed potato rate was calculated as the average percentage of the missed potato mass relative to the total potato mass (picked + missed), as per Equation (17):

$$Y_1={\displaystyle \frac{Q_1}{Q_1+Q_3}}\times 100\%$$

(17)

In the equation, Y₁ is the missed potato rate (%); Q₁ is the mass of missed potatoes (kg); and Q₃ is the mass of mechanically picked potatoes (kg).

(2)

Bruised Potato Rate

After the pickup operation, all potatoes (picked and missed) in each test area were collected and weighed. The bruised potatoes were identified, and their mass was measured. The bruised potato rate was calculated as the average percentage of bruised potato mass relative to the total potato mass, using Equation (18):

$$Y_2={\displaystyle \frac{Q_2}{Q_1+Q_3}}\times 100\%$$

(18)

In the equation, Y₂ is the bruised potato rate (%), and Q₂ is the mass of bruised potatoes (kg).

4.3. Experimental Factor Levels

Based on preliminary theoretical analysis of collisions between the disc harrow bars and potatoes, the rotational speed of the disc directly affects the velocity at which the bars contact the potatoes, thereby influencing bruising during the pickup process. During operation, the forward speed of the machine determines the feed rate of the soil–potato mixture per unit time, impacting pickup efficiency. Additionally, if the tilt angle of the disc is too small, the pickup performance is compromised, whereas an excessive tilt angle increases operational resistance or compromises structural integrity.

In summary, the rotational speed of the pickup disc, tilt angle of the disc, and forward speed of the machine were selected as experimental factors.

Following the Box–Behnken experimental design principle, these three factors were tested with the bruised potato rate and missed potato rate as response variables. The coded levels of the factors are listed in

Table 4. Coding of experimental factors.

Encoding	Factor
	Disc Rotation Speed A (r/min)	Disc Inclination Angle B (°)	Machine Forward Speed C (m/s)
−1	45	14	0.5
0	50	16	0.6
1	55	18	0.7

, and the experimental results are summarized in

Table 5. Experimental program and results.

Test Number	A	B	C	Y1	Y2
1	−1	−1	0	6	6.2
2	1	−1	0	5.8	7.3
3	−1	1	0	7.1	6.5
4	1	1	0	5.9	5.3
5	−1	0	−1	7.5	5.1
6	1	0	−1	6.2	6.3
7	−1	0	1	6.1	5.7
8	1	0	1	5.2	5.1
9	0	−1	−1	7.3	5.5
10	0	1	−1	7.2	3.9
11	0	−1	1	4.4	5.3
12	0	1	1	6.5	4.6
13	0	0	0	2.2	2.5
14	0	0	0	2.3	2.5
15	0	0	0	2.5	2.1
16	0	0	0	1.8	2.2
17	0	0	0	2.2	2.4

.

4.4. Analysis of Experimental Results

The experimental data for the missed potato rate Y₁ and bruised potato rate Y₂ were analyzed using Design-Expert 13 software. Quadratic regression models for Y₁ and Y₂ were established as follows:

$$\begin{array}{l}{Y}_1=2.20-0.45A+0.4B-0.75C-0.25AB+0.1AC+0.55BC\\ +1.95A^2+2.05B^2+2.10C^2\end{array}$$

(19)

$$\begin{array}{l}{Y}_2=2.34-0.0625A-0.5B-0.0175C-0.575AB-0.45AC+0.225BC\\ +2.35A^2+1.63B^2+0.855C^2\end{array}$$

(20)

The ANOVA results for the regression equations are summarized in

Table 6. Analysis of variance table for missed potato rate.

Source	Missed Potato Rate Y1
	Sum of Squares	df	F	P	Significance
Model	67.32	9	87.26	<0.0001	**
A	1.62	1	18.9	0.0034	**
B	1.28	1	14.93	0.0062	**
C	4.5	1	52.5	0.0002	**
AB	0.25	1	2.92	0.1314
AC	0.04	1	0.4667	0.5165
BC	1.21	1	14.12	0.0071	**
A2	16.01	1	186.79	<0.0001	**
B2	17.69	1	206.44	<0.0001	**
C2	18.57	1	216.63	<0.0001	**
Residual	0.6	7
Lack of Fit	0.34	3	1.74	0.2962
Pure Error	0.26	4
Cor Total	67.92	16

** indicates a highly significant effect (P ≤ 0.01).

and

Table 7. Analysis of variance table for bruised potato rate.

Source	Bruised Potato Rate Y2
	Sum of Squares	df	F	P	Significance
Model	45.62	9	91.09	<0.0001	**
A	0.0313	1	0.5616	0.478
B	2	1	35.94	0.0005	**
C	0.0012	1	0.0225	0.8851
AB	1.32	1	23.77	0.0018	**
AC	0.81	1	14.56	0.0066	**
BC	0.2025	1	3.64	0.0981
A2	23.35	1	419.67	<0.0001	**
B2	11.19	1	201.05	<0.0001	**
C2	3.08	1	55.32	0.0001	**
Residual	0.3895	7
Lack of Fit	0.2575	3	2.6	0.1892
Pure Error	0.132	4
Cor Total	46	16

** indicates a highly significant effect (P ≤ 0.01).

.

After removing statistically insignificant terms from the regression models, the optimized quadratic regression equations for Y₁ (missed potato rate) and Y₂ (bruised potato rate) were derived as follows:

$$Y_1=2.20-0.45A+0.4B-0.75C+0.55BC+1.95A^2+2.05B^2+2.10C^2$$

(21)

$$Y_2=2.34-0.5B-0.575AB-0.45AC+2.35A^2+1.63B^2+0.855C^2$$

(22)

From Equations (21) and (22), it is evident that the disc rotational speed (A), disc tilt angle (B), and forward speed (C) of the dual-disc pickup device all influence the missed potato rate (Y₁). However, the bruised potato rate (Y₂) is primarily affected by the disc tilt angle (B).

The interaction between disc tilt angle (B) and forward speed (C) has a highly significant effect on the missed potato rate (Y₁).

The interactions between disc rotational speed (A) and disc tilt angle (B), as well as between disc rotational speed (A) and forward speed (C), exhibit highly significant effects on the bruised potato rate (Y₂).

The contribution degree of each experimental factor to the performance metrics (Y₁) and (Y₂) was determined based on F-values, where a larger F-value indicates a stronger contribution.

For the missed potato rate (Y₁), the order of influence is

Forward Speed (C) > Disc Rotational Speed (A) > Disc Tilt Angle (B).

For the bruised potato rate (Y₂), the order of influence is Disc Tilt Angle (B) > Forward Speed (C) > Disc Rotational Speed (A).

To analyze these interactions further, response surface plots were generated using Design-Expert 13 software to visualize the effects of key factor interactions on Y₁ and Y₂, as shown in Figure 10.

Figure 10a shows the response surface for the interaction between the disc tilt angle (B) and forward speed (C) on the missed potato rate (Y₁). The large curvature of the contour lines indicates that their interaction has a highly significant effect (p < 0.01) on Y₁. With the disc rotational speed (A) fixed at its zero level (50 r/min), when the machine forward speed is low, the missed potato rate first decreases and then increases as the disc tilt angle increases. When the machine forward speed is high, the missed potato rate slightly decreases initially and then rises sharply with an increasing disc tilt angle. As the machine forward speed increases, the overall variation curve of the missed potato rate with the disc tilt angle follows a “decrease-then-increase” pattern. However, when the machine forward speed falls within a reasonable range, the amplitude of the missed potato rate variation is significantly smaller.

Figure 10b shows the response surface of the interaction between the disc rotational speed and disc tilt angle on the bruised potato rate. The contour lines exhibit significant curvature, indicating a pronounced interaction effect between these two factors on the missed potato rate. When the machine forward speed is fixed at the zero level (0.6 m/s), at lower disc rotational speeds, the bruised potato rate first decreases and then increases as the disc tilt angle increases. At higher disc rotational speeds, the missed potato rate first decreases and then increases with the elevation of the disc tilt angle. When the disc rotational speed is 45 r/min, the bruised potato rate ranges between 4.8 and 6.7%; at 55 r/min, the bruised potato rate ranges between 5 and 7.5%. This occurs because the disc tilt angle directly affects the feeding rate of the potato–soil mixture, where soil provides cushioning and protective effects for potatoes. Under the same disc tilt angle, a reasonably matched disc rotational speed results in a lower bruised potato rate. As the disc rotational speed increases, the peak mechanical force on potatoes rises, intensifying collisions between potatoes and the machine, causing the overall bruised potato rate curve to rise. At 55 r/min, the soil’s cushioning effect weakens, leading to a higher bruised potato rate.

Figure 10c displays the response surface of the interaction between the disc rotational speed and machine forward speed on the bruised potato rate. The contour lines exhibit sharp curvature, indicating a pronounced interaction effect between these two factors on the missed potato rate. With the disc tilt angle fixed at the zero level (16°), at a disc rotational speed of 45 r/min, the bruised potato rate initially decreases slightly and then rises as the machine forward speed increases. At disc rotational speeds of 50 r/min and 55 r/min, the bruised potato rate first decreases and then increases with the elevation of the machine forward speed. For disc rotational speeds between 48 and 52 r/min, the bruised potato rate exhibits a relatively flat trend across variations in the machine forward speed.

4.5. Optimization of Parameters

According to the above test indexes, combined with the actual working conditions, the optimization solver in Design-Expert 13 software is used to solve the regression equation by eliminating the insignificant regression terms. Set the following constraints:

$$\left\{\begin{array}{l}\min Y_1(A,B,C)\\ \min Y_2(A,B,C)\\ 45\le A\le 55\\ 14\le B\le 18\\ 0.5\le C\le 0.7\\ 0\le Y_1\le 5\%\\ 0\le Y_2\le 6\%\end{array}\right.$$

(23)

The theoretical optimal solution for the following pickup device parameters is derived: disc rotational speed of 50 r/min, disc tilt angle of 16°, and machine forward speed of 0.6 m/s. Under this parameter combination, the missed potato rate is 1.918%, the bruised potato rate is 2.273%, and the optimization result expectation value is 0.933.

5. Field Trial Validation

5.1. Test Methods and Evaluation Metrics

The field trials were conducted in September 2023 in Jiaozhou, Shandong Province. The soil type is loam with a water content of approximately 17%. The experimental field utilized a large-ridge double-row planting pattern with a ridge spacing of 700 mm, and the potato variety was Xisen No. 6; the average yield of this variety is about 42–45 t/ha. Three days prior to the trials, the vine-killing treatment was applied to the mature potato plots, followed by clearing the ground and ridge furrows. Potatoes were harvested using a potato digger harvester and field-cured for 3 h. The prototype pickup device was coupled with a 4UJD-110 potato pickup and grading machine, powered by a Dongfanghong 1204 tractor. Field performance tests were conducted based on simulation results to verify the reliability of the optimized parameters obtained from the simulation. The entire process adhered to the technical standard DB64/T 1795-2021 “Technical Specification for Mechanized Potato Pickup”. The field trials process is shown in Figure 11.

5.2. Test Results

The comparison between measured and theoretical values is presented in

Table 8. Comparison of measured and theoretical values.

Item	Missed Potato Rate (%)	Bruised Potato Rate (%)
Measured Value	1.53	2.45
Theoretical Value	1.29	2.27
Technical Requirements	≤5	≤6

. Field validation trials demonstrated that the missed potato rate and damaged potato rate both met the requirements, with the relative error between the measured and theoretical values not exceeding 8%.

5.3. Discussion

Field performance tests show that the dual-disc potato picking and harvesting device designed in this paper can achieve a working efficiency of 2 hectares/day, which is nearly 20 times more efficient than manual picking and harvesting, and the damage rate to potatoes meets the technical requirements. Replacing manual picking with this dual-disc potato picking and harvesting device is expected to save over 70% in harvesting costs per hectare.

6. Conclusions

(1)

To address the issues of low efficiency and high cost in manual potato pickup during harvesting, this paper designed a dual-disc potato pickup harvesting device, including key components such as the pickup disc and elevating chain device.

(2)

EDEM-RecurDyn co-simulation was used to simulate the working state of the pickup device. Using Design-Expert software, with the disc speed, disc inclination angle, and machine forward speed as independent variables and the missed potato rate and damaged potato rate as dependent variables, a quadratic polynomial regression model was established. After optimizing the regression model, the optimal operating parameters for the potato pickup device were determined: disc speed of 50 r/min, disc inclination angle of 16°, and machine forward speed of 0.6 m/s.

(3)

Field tests using the optimal parameters yielded a missed potato rate of 1.53% and a damaged potato rate of 2.45%, which met the requirements for potato pickup harvesting operations.

In the kinematic analysis of the picking disc’s working process, this study conducted the analysis under relatively ideal conditions without considering the interaction between soil, potatoes, and the device during the process. Therefore, it is recommended that future research explore the interaction relationships among potatoes, soil, and the device. In the collision analysis, further theoretical studies can be conducted on collision damage under different angles.