The Design and Experimentation of a Wheeled-Chassis Potato Combine Harvester with Integrated Bagging and Ton Bag-Lifting Systems

Abstract

The mechanized harvesting level of potatoes in the arid areas of Northwest China is low and mainly relies on simple machinery to dig the soil surface, and then people manually pick up and bag the potatoes. This harvesting method has the problems of a high labor intensity, low operation efficiency, and high labor cost. Based on this, a wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems was developed, which could complete potato digging, potato–soil separation, potato–film separation, automatic bagging, and field ton bag lifting in one go. Firstly, based on the agronomic requirements and unique terrain characteristics of potato planting in this area, the structural design of the whole machine was completed with SOLIDORKS 2019 3D software. Secondly, the dynamic model was established for a numerical analysis, and the core parameters of key components were determined. The field experiments showed that the potato loss rate was 2.1%, the potato damage rate was 1.7%, the skin breaking rate was 2.5%, the impurity content was 1.9%, and the productivity was 0.15~0.23 hm²/h. The above field test indexes met the requirements of national and industrial standards.

1. Introduction

Potato (Solanum tuberosum L.) is the fourth major food crop in China, which is widely planted in China. In recent years, China’s domestic potato planting area and total annual output ranked first in the world [1,2,3,4,5]. Due to the influence of factors such as a low mechanized potato harvesting level, the complex terrain characteristics of planting areas, and non-standard planting modes, the mechanized potato harvesting rate in China is only 32% [6,7,8,9,10]. The northwest dry area is one of the main potato production areas in China, with the planting area accounting for more than 22% of the total potato area in China [11]. However, the current harvesting method is generally to excavate the crop with simple machinery and leave it on the soil surface and then collect it manually. The harvesting method is extremely rudimentary, resulting in a high labor intensity, low harvesting efficiency, high labor cost, etc. In addition, Northwest China is located in the cold plateau area, and frost damage is easily caused if the harvesting time is too long [12,13]. In addition, due to the serious aging of the rural population in China, there is an urgent need for potato combine harvesters that are suitable for local conditions to solve the current industrial conflicts and to address the weaknesses of mechanized potato harvesting.

In the 1990s, developed countries such as Germany, the United States, Italy, and Poland had already achieved integrated potato combine harvesting technology [14,15,16]. For example, large self-propelled combine harvesters such as the GRIMMER (Damme, Germany) VARITRON 470 from Germany, the AVR (Roeselare, Belgium) Puma 3 from Belgium, and the Ploeger Oxbo (Roosendaal, The Netherlands) AR-4BX from the Netherlands complete the processes of vine killing, digging, separating, loading, and automatic unloading in a single operation. These machines feature advanced technology and a high degree of automation. Additionally, large, trailed combine harvesters such as the Double L (Blackfoot, ID, USA) 7340 from the United States, the SPEDO (Verona, Italia) SPRA-1/J from Italy, and the SANEI (Shizuoka, Japan) EX-ZERO from Japan have also achieved ton bagging and vehicle-following loading operations [9,17,18]. In the arid regions of Northwest China, where fields are small, paths are narrow, and the economic level is low, the large size and high cost of foreign combine harvesters have made it difficult to promote and apply them in this region. The research on potato mechanization technology in China started late, but has made rapid progress, especially with the support of the 13th Five Year Plan. Domestic potato harvesting machinery has been moving from a low level to a medium to high level of research and development. For example, universities and research institutes such as Gansu Agricultural University [2,3], Shandong University of Technology [6], Kunming University of Science and Technology [19], Qingdao Agricultural University, Northeast Agricultural University, the Chinese Academy of Agricultural Mechanization Sciences [15], and Nanjing Research Institute for Agricultural Mechanization Ministry of Agriculture under the Ministry of Agriculture and Rural Affairs have continuously made breakthroughs in potato combine harvesting technology. They have gradually developed research achievements with independent intellectual property rights and are currently in the stage of pilot improvement [19,20,21,22,23,24]. Additionally, well-known domestic enterprises have developed large potato combine harvesters that have been put to use on large farms in regions such as Heilongjiang and Inner Mongolia. Examples include the 3110 and 4UQL-170 models produced by Qingdao Hongzhu Agricultural Machinery Co., Ltd. (Qingdao, China), the self-propelled potato pick-up and bagging machine developed by Menoble Co., Ltd. (Beijing, China), the 4UL-170 series produced by Shandong Stair Agricultural Equipment Co., Ltd. (Deizhou, China), and the 4ULHZ-840 model produced by Suihua Xinyu Machinery Manufacturing Co., Ltd. (Suihua, China) [14].

As mentioned above, the potato combine harvester currently used in China is of large size, difficult to transfer and turn around, and cannot adapt to the mountainous terrain with narrow field paths in the northwest dry area. In addition, the unique film and soil-covering planting mode of potatoes in the northwest arid region results in the poor separation of the potato–soil film and a high impurity content. This article describes the design of a wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems. The machine could complete digging, potato–soil separation, potato–film separation, automatic bagging, field ton bag hoisting, and other work at one time. The whole machine is small in size and easy to transfer and turn around in farmland, which improves the work efficiency and effectively reduces the manual input. The field test indexes meet the national and industrial standard requirements. In addition, the problem of the lifting difficulty of ton packs in the field was solved, and the mechanized harvesting level of potatoes in the northwest dry area was effectively improved.

2. Materials and Methods

2.1. Planting Agronomy and Farmland Characteristics

Figure 1a is a ridge diagram of one ridge and two rows with a black film covering and a soil covering on top of the film. The width of the ridge bottom is 800~900 mm, the height of the ridge is 150~200 mm, and the width of the blank row in the operation is 300 mm. One ridge is planted in two rows with a row spacing of 400 mm. To store water and retain moisture, a black plastic film with a width of 1200 mm and a thickness of 0.01 mm is used for covering. The top of the film is covered with soil to promote the automatic breaking of the film and reduce the phenomenon of seedling burning [25,26]. According to Figure 1b, most of the arid areas in the northwest are dominated by mountainous terraced fields, with farmland distributed in a stepped shape along the contour lines of the mountain slopes. The farmland is narrow and curved, the soil type is mainly loess in loam. In response to the above situation, a wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems was designed, with a wheeled chassis for more convenient transferring and turning.

2.2. Research Method

In order to solve the problem of potato combine harvesting in the northwest dry area, a reverse engineering method was adopted. The overall scheme of the method in this article is shown in Figure 2. In more detail, stage 1: preliminary analysis (actual harvesting conditions); stage 2: determine technical scheme; stage 3: 3D modeling (preliminary design); stage 4: redesign (technical scheme verification); and stage 5: verification (field test). This method has also been integrated into tractor safety design by M. Fargnoli, L. Vita, and others [27], which is sufficient proof of the scientific validity of this approach.

2.3. Overall Structure and Main Parameters

As shown in Figure 3, this machine is composed of a four-wheeled, self-propelled chassis; front harvesting device; lifting hydraulic cylinder; operator’s cabin; electrical lifting device; picking platforms with different paths; a guide groove; ton bag-lifting, rope-tensioning device; foot pedal; ton bag self-unloading platform; a transmission system; etc. The main parameters are shown in

Table 1. Main technical parameters of the homework machine.

Index	Data
Structural style	Wheeled self-propelled type
Engine power (kW)	73.5
Engine rated speed (R·min−1)	2600
Wheel track (m)	1.38
Wheelbase/m	2.2
Minimum turning radius (m)	2.8
Overall machine dimensions: (length × width × height) (m × m × m)	5.6 × 1.78 × 2.8
Working width (m)	1.1
Number of rows harvested	2
Digging depth (m)	0~240
Potato harvest method	Ton bag
Productivity (hm2·h−1)	0.15~0.23

.

2.4. Working Principle

When the machinery entered the field, the front harvesting device was lowered to the working height by controlling the lifting hydraulic cylinder. As the unit moved forward, the mixture of potato, soil, film, and seedlings were excavated and shoveled up and continuously loosened, separated, and transported. Most of the soil, residual seedlings, and residual film were separated out. Potatoes and a small amount of remaining hard soil and debris were thrown to the picking platforms with different paths. There were impurity removal channels on both sides of the picking platforms with different paths. The remaining small amount of soil and debris was sorted and discharged from the machine by the people standing on both sides of the foot pedal. Clean potatoes fell into the rear ton bag through the guide groove. The filled ton bags were lowered and tilted backwards to the ground through the ton bag self-unloading platform. After the field harvest operation was completed, the ton bags in the field were loaded onto other transportation vehicles through the electrical lifting device provided by the machine to complete the transfer. This machine could complete the excavation, separation of potato soil and seedlings, separation of potato film, automatic bagging, and lifting of ton bags in the field in one go.

3. Key Working Units

3.1. Front Harvesting Device

3.1.1. The Structure and Working Principle of the Front Harvesting Device

The front lifting device is a crucial component of the potato combine harvester, primarily consisting of the digging device, the composite separation and lifting device, and the film vine clearing device. As shown in Figure 4, it specifically consists of a front harvesting device frame, a depth-limiting, soil-crushing device, two seedling-cutting discs, a split-type digging device, a grid bar soil-crushing roller group, a rod–chain separation screen, a scraper auxiliary lifting device, a counterweight blocking rod, a flexible sorting roller, etc.

During machine operation, the V-shaped depth-limiting roller in the front depth-limiting, soil-crushing device crosses the ridges for operation, combined with an elastic profiling mechanism which not only plays a role in floating, profiling, and stabilizing the excavation depth, but also crushes the hard soil on the membrane, achieving a good soil-crushing effect. Digging the shovel wedge under the ridge, the entire ridge body is lifted up, and the soil, stems, seedlings, and plastic film are continuously separated through the grid bar soil-crushing roller group, rod–chain separation screen, and the film and seedling removal devices. In order to reduce the longitudinal size of the front harvesting device, the inclination angle θ of the rod–chain separation screen is designed to be larger. In order to prevent the potatoes from rolling back and forth and causing scratches, a scraper auxiliary lifting device is installed, which is consistent with the linear speed of the rod–chain separation screen. The potatoes, residual films, and seedlings are transported to the rear film and seedling removal devices. Under the action of the counterweight blocking the rod and flexible impurity removal roller, the residual films and seedlings are discharged from the machine, and the potatoes and remaining soil blocks are transported to the picking platforms by different paths.

3.1.2. The Split-Type Digging Device

The digging device is a key component of the front harvesting device. As a typical soil-touching component, reducing the digging resistance, improving soil-crushing performance, and high reliability are the key design ideas. The digging device of the wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems adopted a split digging device. It had good drag reduction and soil-crushing performance, and an overload protection mechanism was designed. If the shovel tip encounters a hard object during the digging process, the overload protection bolt will be sheared instantaneously to avoid damage to the digging shovel.

Where L₁ is the length of the digging shovel, (mm); B₁ is the width of the digging shovel, (mm); S is the grass sliding gap, (mm); γ is the digging shovel blade angle, (°); L₂ is the width of split-type digging device, (mm); h is the installation height behind the digging shovel, (mm); f is the friction resistance of the digging shovel, (N); G is the soil gravity on the digging shovel, (N); N_e is the reaction force of the digging shovel on the soil, (N); α is the digging shovel insertion angle, (°); and F_t is the force required by the digging shovel to lift the material along the forward direction, (N).

As shown in Figure 5, The split-type digging device consists of a flat digging shovel, a hinged beam frame, an angle adjustment mechanism, a bracket, and an overload protection frame. The designed L₂ was 1~1.1 m (adjustable), the B₁ was 150 mm, and the S was adjustable from 20~40 mm [28].

In order to ensure the automatic cleaning and sliding cutting function of the digging shovel edge, the angle γ of the digging shovel edge should be satisfied:

$$90-\gamma >\varphi$$

(1)

In the formula, φ represents friction angle of soil to steel. It generally takes 30°~36° [15,19,25], and the γ angle of the digging shovel was designed to be 45°, which meets the operational requirements.

The L₁ depends on the h and α. The h from the ground behind the digging shovel depends on the installation height of the grid bar soil-crushing roller I and the position of the digging shovel bracket. In the front harvesting device, the designed h behind the excavation shovel from the ground was about 150~192 mm.

The relationship between the L₁ and the height h of the rear end of the digging shovel from the ground is shown as follows:

$$L_1={\displaystyle \frac{h}{\sin \alpha }}$$

(2)

In addition, the traction resistance of the excavator shovel is greatly affected by soil type, excavation depth, excavation shovel form, and excavation shovel inclination angle, and the following relationship can be established [2,3,29]:

$$\left\{\begin{array}{l}{F}_{\mathrm{t}}\cos \alpha -f-G\sin \alpha =0\\ N_{\mathrm{e}}-G\cos \alpha -F_{\mathrm{t}}\sin \alpha =0\end{array}\right.$$

(3)

In the formula, ε represents the friction coefficient of the soil + potato + seedling mixture on the excavator shovel, ε = tan φ. By calculation, the digging shovel insertion angle is as follows:

$$\alpha =\arctan {\displaystyle \frac{F_t-\epsilon G}{\epsilon F_t+G}}$$

(4)

Field experiments have shown that the length of the digging shovel could easily lead to blockage. In addition, due to the limitation of the h, the α was designed to be 30° to 40° (adjustable). After calculation and analysis, it was determined that L₁ was 300 mm.

3.1.3. The Composite Separation and Lifting Device

In order to shorten the longitudinal size of the front harvesting device, balance the center of gravity of the entire machine, and improve the separation effect, the front harvesting device adopts the idea of “short path, large inclination angle, first crushing soil, and then separating”, and we designed a composite separation lifting device. As shown in Figure 6, the composite separation and lifting device consists of a grid bar soil-crushing roller group, a rod–chain separation screen, a high-frequency, low-amplitude vibration device, and a scraper auxiliary lifting device.

Where R₁ is the radius of the grid crusher roller, mm; n₁ is the speed of the grid crusher roller, r/min; v₂ is the linear speed of the rod–chain separation screen, m/s; n₂ is the driving shaft speed of the rod–chain separation screen, r/min; R₂ is dividing radius of the driving wheel of the rod–chain separation screen, mm; n₃ is the driving shaft speed of the scraper auxiliary lifting device, r/min; R₃ is the scraper rotation radius, mm; v₃ is the linear speed of the scraper auxiliary lifting device, m/s; L₂ is the effective length of the composite separation lifting device; θ is the inclination angle of the rod–chain separation screen; and H_min is the minimum installation height at the rear end of the rod–chain separation screen.

If the separation path of the front harvesting device was short and relies solely on the rod–chain separation screen for potato–soil separation, it would not meet the requirements. The split-type digging device lifted the ridge, but the ridge body was not completely crushed, with potatoes still wrapped in a large amount of soil, providing good protection for the potatoes. Therefore, two sets of grid crusher rollers were added in front of the rod–chain separation screen to avoid damaging the potatoes, enhance soil crushing, and accelerate potato–soil separation. The pitch of the grid crusher roller and the rod–chain separation screen were both designed to be 50 mm, with the relationship of the pitch circle radius as follows:

$$R_1=R_2={\displaystyle \frac{PZ}{2\pi }}$$

(5)

In the formula, P is the pitch of the grid crusher roller and the rod–chain separation screen, taken as P = 0.05 m, and Z is the number of teeth of the rod–chain separation screen driving wheel and the number of grid crusher rollers, taken as Z = 8.

For the sandy loam soil type in the northwest arid region, the v₂ should be designed to be about 1.2~1.6 m/s [28]. To avoid the blockage of the potato soil mixture on the screen surface, the line speed of the grid crusher roller and the rod–chain separation screen should be basically the same. Therefore, the n₁ and the n₂ meet the following relationship:

$$n_1=n_2={\displaystyle \frac{30v_2}{\pi R_2}}$$

(6)

In addition, as shown in Figure 6, the relationship between the L₂ and the θ is as follows:

$$L_2={\displaystyle \frac{H_{\min }}{\sin \theta }}$$

(7)

The H_min is limited by the four-wheel, self-propelled chassis and the picking platforms with different paths. Considering the overall layout structure, the H_min was designed to be 1150 mm, in order to reduce the longitudinal size of the machine as much as possible; the θ was designed to be 42°; the L₂ was calculated to be about 1720 mm. According to the literature, the limit inclination angle θ_max of the rod–chain separation screen with a pitch of 50 mm was 27.34° [2]. To prevent damage caused by potato chunks rolling off the screen surface, a scraper auxiliary lifting device is installed above the rod–chain separation screen. In order to avoid potato injury, the linear speed of scraper should be consistent with the linear speed of the rod–chain separation screen. The n₃ is as follows:

$$n_3={\displaystyle \frac{30v_2}{\pi R_3}}$$

(8)

In this machine, the rotating diameter of the scraper auxiliary lifting device was designed to be 350 mm; therefore, R₃ was taken as 0.175 m. By computing, R₁ = R₂ = 0.0635 m, n₁ = n₂ = 180~240 r/min, and n₃ = 66~87 r/min.

3.1.4. The Film and Vine Clearing Device

In the northwest arid region, potatoes are mainly planted with plastic film to preserve moisture and increase yield. The removal of the residual film and stems is also keyin harvesting [30]. Therefore, it is necessary to design a plastic film and seedling removal device.

Where n₄ is the rotational speed of flexible impurity removal roller, r/min; R₄ is the radius of the flexible impurity removal roller, mm; δ₁ is the gap between the counterweight blocking rod and the rod–chain separation screen, and mm; δ₂ is the cleaning gap, mm.

As shown in Figure 7, the film and vine clearing device consists of 6 sets of counterweight blocking rods, a hinged rod, limit rod, comb film teeth, a flexible impurity removal roller, and film-clearing knife. When the machine was in operation, the rod–chain separation screen transported the plastic film and vines to the counterweight blocking rod. Under the counter-rotating movement of the rod–chain separation screen and the flexible impurity removal roller, the plastic film and vines were discharged from the machine through the gap between the rod–chain separation screen and the flexible impurity removal roller. The comb film teeth prevented the plastic film from wrapping around the scraper auxiliary lifting device, and the film-cleaning knife continuously cleaned the plastic film and vines wrapped around the flexible impurity removal roller. The limit rod restricted the position of the counterweight blocking rod. In order to avoid blockage of the plastic film and vines, the speed n₄ of the flexible impurity removal roller must meet the following relationship with the speed n₂ of the active shaft of the rod–chain separation screen:

$$n_2{R}_2\ge n_4{R}_4$$

(9)

The above has determined that n₂ = 180~240 r/min, R₂ = 63.5 mm. If the speed of the flexible cleaning roller was too high, it would be easy to scratch potatoes, so the minimum speed of the flexible impurity removal roller n₄ was calculated to be 265 r/min. In addition, the δ₁ was designed to be 20~35 mm (adjustable), and the δ₂ was designed to be 15~30 mm (adjustable).

3.2. Picking Platforms with Different Paths

The potatoes, hard soil blocks, vines, and film that are harvested through the front harvesting device need to be mechanically and manually cleared for a second time through the picking platforms with different paths. As shown in Figure 8, the picking platforms with different paths mainly consist of a frame, a baffle plate, a secondary rod–chain separation screen, a guiding groove, a hydraulic transmission system, and a dust shield. When the machine was working, potatoes and residual debris flowed into the sorting channel entrance and continued to be transported backwards by the secondary rod–chain separation screen. The staff standing on both sides of the picking platforms with different paths manually moved the soil blocks and vines in the sorting channel to the impurity removal channel. Clean potatoes continued to flow backwards through the sorting channel into the guide groove and into the ton bag. The secondary rod–chain separation screen was driven by a hydraulic motor for operation. The speed of the secondary rod–chain separation screen could be manually infinitely changed from 0 to 96 r/min through a speed control valve. If necessary, three modes of clockwise rotation, counterclockwise rotation, and shutdown could be selected through a manual switching valve. In addition, an engine was installed below the picking platforms with different paths, and the dust shield provided protection.

Where B_Z is the width of the secondary rod–chain separation screen, mm; B_F is the width of the middle sorting channel, mm; and B_P is the width of the impurity removal channel, mm.

The B_Z was designed to be 900 mm, the B_P was 200 mm, and the B_F was 500 mm. During work, for the convenience of manual sorting and safety, the maximum line speed of the secondary rod–chain separation screen was 0.75 m/s. Therefore, the driving shaft speed of the secondary rod–chain separation screen was

$$v_6={\displaystyle \frac{n_7\pi R_8}{30}}\le 0.75$$

(10)

Obtained

$$n_7={\displaystyle \frac{30v_6}{\pi R_8}}$$

(11)

where v₆ is line speed of the secondary rod–chain separation screen, m/s; n₇ is revolution speed of secondary rod–chain separation screen drive shaft, r/min; and R₈ is radius of secondary rod–chain separation screen, taken as 75 mm.

According to the Formulas (10) and (11), when working, the maximum speed n₇ was 96 r/min.

As shown in Figure 8, the driving shaft of the two-stage rod–chain separation screen is driven by a hydraulic motor, used a cycloidal hydraulic motor BM1-200 (Like, Jining, China). The displacement of the hydraulic motor is 200 mL/r. The flow rate and power of the motor during operation are as follows:

$$q_m={\displaystyle \frac{n_7{V}_m}{{\eta }_v}}\times {10}^{-3}$$

(12)

$$P_{om}={\displaystyle \frac{2\pi n_7{T}_m}{60}}\times {10}^{-3}$$

(13)

where Q_m is hydraulic motor flow rate, L/min; V_m is hydraulic motor displacement, 200 mL/r; η_V is volumetric efficiency, take as 0.9; P_om hydraulic motor output power, kW; and T_m is working torque, N·m.

After measurement, the required torque T_m of the secondary rod–chain separation screen was about 60 N·m. The required flow rate q_m of the hydraulic motor was calculated to be 21.3 L/min, by Formulas (12) and (13), and the output power P_om was 0.6 kW.

3.3. Ton Bag Self-Unloading Platform

As depicted in Figure 9, the ton bag self-unloading platform encompasses a track gantry, a tilting action hydraulic cylinder, a lifting action hydraulic cylinder, a ton bag-lifting, rope-tensioning device, a small wheel frame, and a roller platform. During the operation of the machine, we suspended the ton bag sling on the hook and tensioned the lifting rope through the action of the tension spring to keep the entrance of the ton bag constantly open, facilitating the entry of potato blocks into the bag. The lifting hydraulic cylinder enables the height of the roller platform to be adjusted at any time, facilitating the unloading of the ton bag. Furthermore, the height of the roller platform can be manually regulated to control the drop height of the potatoes, preventing collision damage among the potato blocks caused by an excessively high drop height. When the ton bag was filled to capacity, the lifting action hydraulic cylinder was slightly elevated, the lifting rope was detached, and subsequently, by manipulating the tilting action hydraulic cylinder, the track door frame, the small wheel frame, and the idler platform were inclined backward, causing the ton bag to automatically drop to the ground. The specific parameters of the ton bag self-unloading platform are presented in

Table 2. Parameters of the ton bag self-unloading platform.

Index	Parameter
Adapt to the size of ton bag (length × width × height)/(m × m × m)	0.8 × 0.8 × 1
Rope form	Double-ring
Roller platform minimum ground clearance (mm)	200
Roller platform maximum ground clearance (mm)	520
Lifting action hydraulic cylinder travel (mm)	320
Tilting action hydraulic cylinder travel (mm)	100
Roller platform maximum tilt angle (°)	15
Hydraulic cylinder control mode	Electrical control

below.

3.4. Electrical Lifting Device

After a piece of farmland is harvested, in general, the ton packaging truck in the field is mostly filled with the help of special lifting equipment, resulting in a high cost and low utilization. Ssecondary entry can easily damage the soil structure. Therefore, an electrical lifting device is installed on the combine harvester to solve the field lifting problem. As shown in Figure 10, the electrical lifting device consists of a column, a set screw, a winch motor, a lifting beam, a steel wire hook, a controller, etc. The column is fixed to the frame by bolts and U-shaped card.

In general, the maximum weight of ton bags filled with potatoes is about 800 kg, the bag-lifting speed is about 6 m/min, and the drum radius R_j is designed to be 0.075 m. Therefore, the relationship between the actual power and speed of the winch motor is as follows [31]:

$$P_S={\displaystyle \frac{Q_S{v}_d}{60\times 1000{\eta }_c}}={\displaystyle \frac{M_{d}g{v}_d}{60\times 1000{\eta }_r}}$$

(14)

$$n_j={\displaystyle \frac{30v_d}{60\pi R_j}}$$

(15)

where P_S is the actual required power of the winch motor, kW; Q_S is rated lifting capacity, Q_S = M_d, g = 7840 N; V_d is lifting speed, m/min; M_d is a ton of packaging after full total mass, kg; g is acceleration of gravity, g = 9.8 N/kg; h_r is mechanical transmission efficiency, taken as η_r = 0.8; and R_j is roller radius, taken as R_j = 0.075 mg.

Through calculation, the actual working power required was determined to be approximately 0.98 kW, and the actual working speed of the roller was approximately 13 r/min. Therefore, a 12 V permanent magnet DC deceleration motor was selected, with a rated power of about 1.4 kW, which meets the technical requirements and has a certain power reserve. The rated speed of the motor was 2400 r/min, and the three-stage planetary gear deceleration system was adopted. The reduction ratio is 185:1.

Estimation of the maximum tensile force of steel wire

$$S_{\max }={\displaystyle \frac{Q}{K\mathrm{m}{\eta }_{\mathrm{z}}{\eta }_{\mathrm{d}}}}$$

(16)

where S_max maximum tensile force of steel wire, N; K is roller coefficient of a single roller, taken as K = 1; m is the pulley set multiple, taken as m = 2; η_z and η_d are the efficiency of the pulley group and guide pulley, as well as the efficiency of the sliding bearing, and are both taken as 0.92.

Estimation of minimum diameter of wire rope

$$d=c\sqrt{S_{\max }}$$

(17)

where d is wire diameter, mm; c is steel wire selection coefficient, taken as c = 0.104; and S_max is the maximum tension of steel wire, N

By calculation, the maximum tensile force S_max of the steel wire was determined to be approximately 4631 N, and the minimum diameter d of the steel wire was approximately 7.072. Therefore, the diameter d of the steel wire rope was taken as 8 mm. The lifting beam can rotate 360° to adjust the optimal lifting position, and the motor is directly connected to the onboard power supply for use. In addition, the motor comes with an intelligent control module, which has an emergency self-braking function and can automatically stop after detecting a power outage.

4. Results

4.1. Experimental Conditions

In early October 2023, a field harvest experiment was conducted at the potato planting base in Taiping Village, Lujiagou Town, Dingxi City, Gansu Province. The experimental field consisted of two terraced fields with a total area of approximately 0.667 hectares. The planting mode was one ridge, two rows planting with film mulching and soil covering. The planting variety was Longshu 10, and the absolute moisture content of the soil in the field ridge was about 14.3%. The machine harvesting scene and the harvest effect are shown in Figure 11.

4.2. Test Scheme and Method

According to the standards of JB/T 14285-2022 “Potato Harvesting Machinery” and NY/T 648-2015 “Technical Specification for Quality Evaluation of Potato Harvesters”, the working performance of the wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems was tested [32,33]. We mainly measured the potato loss rate, potato damage rate, skin breaking rate, and impurity content during the harvesting process, and we also tested the working conditions of the wheeled, self-propelled chassis; front harvesting device; picking platforms with different paths; automatic loading and unloading platform for ton bags; transmission system; etc.

According to the above standard requirements, the length of the selected testing area shall not be less than 50 m, and the length of the stable areas at both ends shall be set at 10 m. The width of the testing area shall be more than 8 times the working width. During the experiment, multiple round-trips were measured, and three testing areas were randomly selected for each trip. Each testing area was 3 m long, and the width was the working width of the machine. At least 10 repetitions of the experiment were conducted, and the experimental data were measured, and the average value of the repeated experiment measurement results was calculated. According to the above standards, the algorithms for loss rate, damaged potato rate, broken skin rate, and impurity content rate are as follows:

$$L_1={\displaystyle \frac{Q_1+Q_2}{Q}}\times 100\%$$

(18)

$$L_2={\displaystyle \frac{Q_3}{Q}}\times 100\%$$

(19)

$$L_3={\displaystyle \frac{Q_4}{Q}}\times 100\%$$

(20)

$$L_4={\displaystyle \frac{Q_5}{Q_5+Q_6}}\times 100\%$$

(21)

$$Q=Q_1+Q_2+Q_6$$

(22)

where L₁ is potato loss rate, (%); L₂ is potato damage rate, (%); L₃ is skin breaking rate, (%); L₄ is impurity content, (%); Q₁ is mass of missed potatoes, (kg); Q₂ is the mass of missed excavated potatoes, (kg); Q₃ is the mass of damaged potatoes, (kg); Q₄ is the mass of peeled potatoes, (kg); Q₅ is impurity mass, (kg); Q₆ is harvested potato mass, (kg); and Q is total potato mass, (kg).

4.3. Analysis of the Field Experiment Results

The field experiment results for the wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems are shown in

Table 3. Results of field experiments.

Determination Standard	Technical Standard	Tests the Result
Potato loss rate (%)	≤3	2.1
Potato damage rate (%)	≤2	1.7
Skin breaking rate (%)	≤3	2.5
Impurity content (%)	≤4	1.9

.

5. Discussion

According to Table 3, the results showed that the wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems has passed field experiments and determined that the loss rate, potato damage rate, skin breakage rate, and impurity content all meet the national and industry standard requirements. The operation of each component of the equipment was relatively stable, with no other faults except for some mechanism test adjustments. The four-wheel steering system had a small turning radius in the field, which had obvious advantages. The average production rate was about 0.15~0.23 hm²/h. In addition, at present, the potato harvest in northwest arid areas mainly adopts the step-by-step harvesting method, that is, the potato is excavated and laid on the soil surface by simple excavation machinery, and then the final harvest is completed by manual picking and bagging and manual handling to the transport vehicle. Typical harvesting machines such as the 4U-1600 set of pile-type potato diggers (SANNIU, Dingxi, China) were designed by Yang Xiaoping and others [34]. The performance of the two machines was compared and analyzed. The performance indicators are shown in

Table 4. Working performance of two potato harvesters.

Performance Index	Potato Harvesting Machine
	This Harvester	4U-1600 Set of Pile-Type Potato Digger
Productivity (hm2·h−1)	0.15~0.23	0.35~0.55
Potato damage rate (%)	1.7	3.36
Skin breaking rate (%)	2.5	/
Potato obvious rate (%)	Automatic bagging	95.11
Impurity content (%)	1.9	/

.

Although the 4U-1600 set of pile-type potato digger has better productivity than the machine studied in this research, the potato combine harvester described in this article can achieve the automatic bagging of potatoes and can also achieve a ton bag-lifting function, with a high level of mechanization. However, the 4U-1600 set of pile-type potato digger adopts a step-by-step harvesting method, which requires a large amount of manual picking and transportation in the later stage, increasing labor costs. Moreover, the picking efficiency in the later stage is relatively low, significantly reducing the overall harvesting efficiency. In addition, the potato damage rate of the harvester designed in this research is significantly lower than that of the 4U-1600 set of pile-type potato digger, confirming that the key components of this study have good damage reduction performance. After a thorough comparison and analysis, this research has enhanced the mechanized harvesting efficiency of potatoes in the arid regions of Northwest China and effectively reduced harvesting costs.

6. Conclusions

Based on the working conditions of potato farming in the arid area of northwest China, a wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems was designed. This machine completes the processes of soil excavation, potato soil separation, potato film separation, the automatic bagging of potatoes, and the lifting of ton bags in the field in one operation. The whole machine has a compact structure, small longitudinal size, low center of gravity, and good climbing performance. We performed this study in order to provide reference for the mechanized harvesting of potato in hilly and mountainous areas of Northwest China.

• Based on the agronomic requirements and topographical characteristics of potato planting in the northwest arid region, the overall design scheme of the whole machine is determined. The key components are designed and analyzed by SOLID2019 3D software and a dynamic analysis model. The structure and working parameters of the split-type digging device, composite separation and lifting device, the film and vine clearing device, the picking platforms with different paths, the ton bag self-unloading platform, and the electrical lifting device were determined, which improved the potato harvesting quality and the reliability and adaptability of the key components.
• Field experiments have shown that the loss rate of the wheeled-chassis potato combine harvester with integrated bagging and ton bag-lifting systems is 2.1%, the potato damage rate is 1.7%, the skin breaking rate is 2.5%, the impurity content is 1.9%, and the productivity is about 0.15~0.23 hm²/h. The field performance test indicators all meet the national and industry standards requirements. The potato harvesting machine described in this article has a high degree of mechanization and good harvesting performance, which effectively improves work efficiency and saves a lot of labor costs, playing a good role in promoting the development of the potato industry in the arid areas of Northwest China.