Analysis and Evaluation of the Experimental Effect of Double-Disc Knife-Cutting Device for Carrot Combine Harvester

Abstract

At present, the problems of the low cutting reliability and poor cutting quality of carrot harvesters in China are particularly prominent, directly leading to the problems of high root and stem damage rates, low stem and leaf cutting rates, and low cutting surface flatness rates. In order to solve these problems, we developed a disc-type double-disc cutting device. Based on the structural analysis and the central combination design theory of Box–Behnken, using three factors as influencing factors, namely, clamping and conveying speed, the rotary speed of the disc cutter, and the thickness of the disc cutter. A response surface experiment was carried out to analyze the influence of each factor on the high damage rates of the rhizome, the clean rates of stems and leaves, and the flatness rate of cutting surfaces to optimize the influencing factors. According to the test results, a regression mathematical model between test parameters and performance indexes was established, and optimization verification was carried out according to the regression model between test factors and indexes. Finally, the optimal parameter combination is as follows: a clamping and conveying speed of 1.0 m/s, a rotary speed of the disc cutter of 193.5 r/min, and a thickness of the disc cutter of 3.6 mm. The results of the field experiment showed that the root and stem damage rate was 2.61%, the stem and leaf-cutting rate was 87.32%, and the cutting surface flatness rate was 89.87%. Compared with a set of parameters commonly used in double-disc cutters to harvest carrots under the same conditions, the corresponding root and stem damage rates, stem and leaf-cutting rates, and productivity decreased by 2.16%, 1.97%, and 1.87%, respectively, and the comprehensive performance was obviously improved. The proposed research method can well simulate the cutting process in carrot harvesting and provide support for the development of carrot harvesting equipment.

1. Introduction

China’s carrot planting area and export production are perennial first in the world. It is one of China’s most important cash crops, but China’s carrot mechanized harvesting level is relatively lagging behind. In the existing machine operation process, there are a lot of problems, including the low reliability of the double-disc knife-cutting device. Poor cutting quality is particularly prominent, and the problem directly leads to a high carrot root and stem damage rate, a low rate of stem and leaf cut and low cutting surface leveling rate, and so on. This problem directly leads to the high damage rate of carrot roots and stems, low net rate of stems and leaves, and low levelling rate of the cutting surface, which triggers a lot of carrot growers to worry about the quality of carrot harvesting and anxiety, and this problem directly restricts the development of the carrot industry. Therefore, it is of great industrial significance to solve the problem of the operation quality of the double-disc knife-cutting device [1,2,3].

Judging from the international research and development in the field of vegetable harvesting and root cutting, Europe, America, Japan, and other countries started early and developed quickly [4]. At present, European and American countries have developed a variety of different types of carrot combine harvesters, such as the double-row self-propelled carrot combine harvester developed by the German Grimo Company. After cutting using the cutting device, the cutting surface of carrot stems and leaves is flat, with little damage and high working efficiency, which can reach 0.15 hm²/h. However, this combine harvester can only harvest ridge-planted carrots with row spacing of 100 mm, and the application scope of the machine is small [5]. For example, the tassel-fruit separating parts of carrot harvesters developed by Japan’s KUBOTA Company and Denmark’s ASA-LIFT Company all adopt disc-cutter-type separating mechanisms. The main working principle of the separation device is to drive the rotating shaft and the staggered disc cutter to rotate through chain transmission, and when the tassel enters the cutter, the cutting is realized. The device has the characteristics of high efficiency and smooth cutting, but the cutter is susceptible to wear and tear, difficult to disassemble, and can easily injure carrots by accident. In the cutting research of other crops, El Didamony et al. [6] developed a cabbage root-cutting device, carried out experiments, and studied the effects of cutter head shape, cutter speed, and cutter angle on the performance of the harvester. Mathanker S K et al. [7] analyzed the high-speed cutting process of stems and obtained the changing rules of cutting stress, strain, and cutting force.

From the point of view of the development and current situation of carrot harvesting technology in China, Chinese scholars have made some progress in carrot harvesting research in recent years. Xu (2021) [8] used Abaqus software to establish a finite element collision model of the carrot and the horizontal trolley bar and used post-processing software to observe the results of the visualization and export effective data based on the measured yield stress to obtain the simulation state of the collision damage of the carrot critical impact force of the two collision damage factor analysis and the proposed damage reduction measures. Jin et al. (2016) [9] optimized the design of a carrot double-disc cutting device for the problem of low carrot harvesting net rate and seedling cutting rate, and the results show that when the machine forward speed is 1.34 m/s (with a corresponding disc knife speed of 314 r/min), the carrot harvesting net rate is 98.3%, the seedling cutting rate is 90.6%, the fleshy root damage rate is 1.8%, and the total loss rate is 3.5%, which meets the harvesting technical index requirements. Zeng (2023) [10] designed a servo-motor-driven pull-type carrot root and stem separation test bed for the pull-type carrot harvester, which had the problems of high damage rate of carrot roots and stems and poor effect of root and stem separation. With the rotational speed of the driving disc, acceleration of the pulling rod and the angle between the pulling rod and the conveyor belt as the test factors, and the success rate of carrot rhizome separation and the damage rate of carrot rhizomes as the response values, a three-factor and three-level test was designed with the Box–Behnken test method using the Design-Expert 8.0 software, and the regression mathematical models of the factors and the success rate of carrot rhizome separation and the damage rate of carrot rhizomes were established. The regression mathematical models of each factor and carrot rhizome separation success rate and carrot rhizome damage rate were established. Zhao (2024) [11] constructed a digging shovel–carrot–soil discrete element simulation model to address the problem of a high carrot leakage rate, selected the length and width of the digging shovel surface and shovel blade inclination as the test factors, took the digging resistance and soil fragmentation rate as the test indexes, and carried out a carrot digging simulation test. Through this test, the relevant structural parameters and working parameters were analyzed in depth. Liu (2019) [12], in order to study the optimal structural parameters of the carrot harvester, took the green carrot as the research object, used the discrete element software EDEM to simulate and analyze the digging process of the green carrot, determined the power of the digging part and the mechanical strength, and finally carried out the optimal design of the key component parameters of the carrot combine harvester. Lu (2016) [13] designed a new type of V-shaped roller-type counter-top component for the problem of unclean cutting and high damage rate during carrot harvesting, and the test results showed that the device can greatly reduce the rate of injury to the fruit, which provides a theoretical basis for the successful development of a carrot combine harvester. Guan (2020) [14], for a carrot harvesting process where the carrot root damage rate was high, with a low rate of stem and leaf cut net problem, combined with common carrot varieties of material characteristics, developed a bionic single-disc-type cutting device against the top and a device for the structural design and theoretical analysis; the test results showed that the carrot root damage rate was 0.61% and the rate of stem and leaf cut net was 94.93%.

Current international carrot harvesting research exhibits three characteristics. First, some studies employ discrete element simulation models. These models simulate key component structures during harvesting. Simulation results guide parameter optimization processes. This approach facilitates subsequent design improvements [15,16]. Second, mechanical design perspectives drive structural enhancements. The parameters of digging mechanisms are systematically optimized. Both structural and kinematic factors are considered. Third, limited research exists on harvesting equipment. Particularly, relationships between core components remain understudied. Cutting device impacts on quality require deeper investigation.

This study innovatively evaluates harvesting quality parameters. Focus centers on disc-cutting device performance. The objectives address China-specific harvesting challenges. Root and stem damage reduction is prioritized. Stem and leaf cutting quality improvements are targeted. Harvesting process optimization forms the core goals.

Practical development faces two primary obstacles. First, planting modes exhibit significant diversity. China’s main carrot regions include Shandong Province. Sichuan and Anhui are also major production areas. Inner Mongolia also contributes substantially. Regional topography creates climatic variations. These differences necessitate distinct planting patterns.

Agronomic characteristics fundamentally determine equipment design parameters, while physical plant properties directly inform cutting device development. Chinese carrot cultivation employs two primary methods, ridge planting and flat planting, which dominate agricultural practices across production zones. Significant regional variations exist in ridge configurations, row spacing, plant spacing, and planting density, all of which reflect localized agricultural practices. Cultivar selection further complicates standardization efforts.

The lack of standardized agronomic practices and corresponding technical guidelines poses significant challenges for cutting device research. Additionally, the absence of stable and reliable machinery exacerbates these issues. Current cutting devices used in European and American carrot harvesters demonstrate poor adaptability to Chinese planting agronomy while imposing prohibitive costs. Existing imported machinery fails to address three critical performance limitations: high root damage percentage, low stem/leaf cutting efficiency, and inconsistent cutting surface flatness. Therefore, developing solutions requires integrating China’s unique carrot cultivation characteristics with established research and development foundations.

2. Materials and Methods

2.1. Test Bench

The test bench mainly includes the designed double-disc knife-cutting device and the constructed device test bench, whose working principle diagram is shown in Figure 1. The test bench mainly consists of grain lifter, clamping and conveying device, cab, double-disc knife-cutting system, carrots after cutting stem and leaves, collection device, chassis, carrot, carrots with stem and leaves in the field. The working process is as follows: in the process of machine travelling, the carrot stems and leaves will be lifted up by the harvest supporting device, and, at the same time, the digging shovel completes the excavation and loosening the soil under the ground; the plant enters the clamping device and is lifted up and transported upwards by the rubber clamping belt, and the plant will be transformed into another horizontal clamping belt and transported backward horizontally when it is transported to a certain height; in the horizontal transporting process, the plant enters into the cutting device formed by the double-disk knife blades to complete the separation of roots and leaves, and the stems and leaves are cut off. During the horizontal conveying process, the plant enters the cutting device composed of double-disc blades to complete the root and leaf separation, the cut stems and leaves are transported away by the conveyor belt and thrown to the ground, and the carrot fruits fall into the collection device to complete the harvest process.

Table 1. Structural parameters of the test bench.

Parameters	Values
Boundary dimension (length × width × height)/(mm × mm × mm)	4450 × 2015 × 2540 mm
Rated power of engine/kW	33.8
Rated engine speed/(r × min−1)	2400
Working width/m	2.2
Efficiency/(hm2·h−1)	0.19

shows the structural parameters of the test bench.

2.2. Double-Disc Cutting Mechanism Design

The cutting mechanism is mainly divided into reciprocating and rotary types according to the cutting mode. Based on the physical characteristics of carrot stems and leaves, which are high and numerous, the rotary type is chosen to reduce the cutting resistance and lower the loss rate caused by vibration. The disc configuration is divided into single disc and double disc; the single-disc cutting mechanism feeding capacity is poor, generally only used in the clamping conveyor feeding harvester, so the cutting device adopts a double-disc cutting mechanism. The carrot double-disc knife-cutting device designed in this study is shown in Figure 2. The device mainly consists of core components, such as drive gear, drive chain, left disc knife, right disc knife, sleeve and bevel gear, etc. The device is mainly composed of core components, such as driving gear (45 Gr material), driving chain (45 steel material), left disc cutter (CR12MOV material), right disc cutter (CR12MOV material), sleeve (Q235 steel material) and bevel gear (45 Gr material). The 7GU-20K cutter driving motor and the D180M-0120030B-E motor of the clamping and conveying device are customized special speed-regulating motors. They are able to accurately meet the stringent demands on the rotational speed of the disc knives and the variation in the linear speed of the clamping conveyor belt during the test, thus ensuring the accuracy and reliability of the test.

During the test, the double-disc knife-cutting device is precisely fixed under the carrot stem and leaf clamping conveyor of the test bench. The driving motor of the clamping conveyor provides stable and continuous power to the clamping conveyor belt, which enables the carrot stems and leaves to be smoothly clamped and transported upwards to the double-disc knife-cutting device. The carrot stems and leaves are neatly pulled together by the precise coordination of the clamping conveyor belt and the top mechanism of the double-disc knife-cutting device. Subsequently, the disc knife drive motor drives the disc knife gear shaft to operate efficiently, which in turn drives the disc knife to rotate rapidly, thereby accurately completing the cutting process of the carrot stems and leaves.

As one of the important components of the carrot double-disc cutting device, the disc knife structure and movement parameters significantly affect the carrot harvesting effect. This study focuses on the calculation of the disc radius, disc overlap, disc structure and disc speed.

2.2.1. Damage Rate Measurement Method

The carrot stem and leaf cutting process is divided into the cutting contact stage and cutting stage. In the cutting contact stage, the structural parameters of the disc cutter have a greater impact on the stem and leaf contact force. The stem and leaf are subject to the disc acting on the stem and leaf N₁, N₂ two forces. In order to facilitate the analysis, this study will approximate the carrot stem and leaf clusters as a circle, then the stage of the stem and leaf force, as shown in Figure 3.

To make the carrot stems and leaves enter the disc knife and be cut off at one time, it is necessary to satisfy that the clamping force of the knife disc is greater than the pushing force on the stems and leaves. And no slip in contact with the knife disc should satisfy Formula (1):

$$\left\{\begin{array}{l}{F}_0>N_{1}sin\beta +N_{2}sin\beta -F_{1}cos\beta -F_{2}cos\beta \\ cos\beta ={\displaystyle \frac{a}{2(r_k+r_j)}}\end{array}\right.$$

(1)

Here, F₀ is the tensile force in the conveying direction of the stalk-gripping mechanism, N; F₁ is the left tangential slip force, N; F₂ is the right tangential slip force, N; β is the angle between the normal thrust and the line to the center of the blade, (°); a is the center distance between the two cutters, mm; r_k is the radius of disc cutter, mm; and r_j is the maximum contour radius of the carrot stem and leaves, mm.

Based on the measurements of the physical properties of carrot stems and leaves, the geometric relationship between the shear angle and the radius of the cutter and the horizontal distance from the center of the cutter can be obtained from Formula (2):

$$\beta =\arccos ({\displaystyle \frac{r_k-l/2}{r_k+r_j}})$$

(2)

Here, l is the overlap width of the cutter disc, mm.

In order to avoid leakage and reduce the loss caused by the collision of the two sides of the carrot recycling mechanism on the plant, each row of carrots corresponding to the cutting mechanism of the overall width of the whole plant should be greater than the diameter of a single plant (the whole plant), with a carrot bush contour diameter of about 180 mm; for the arrangement of the recycling mechanism, each row of carrots corresponding to the overall width of the carrot cutting mechanism of the whole plant should be no greater than the row spacing of 300 mm, and the relationship between the formula is in line with Formula (3):

$$180<4r_k-l\le 300$$

(3)

Utilizing (1)–(3), combined with the relevant geometric conditions, the overlapping width l of the cutter head is 78 mm and the radius r_k of the disc cutter is 95 mm.

2.2.2. Motion Parameter Design

After the disc cutter contacts the stem and leaves, it clamps the stem and leaves for cutting, and at the same time produces the thrust in the forward direction. Under the thrust F_x in the forward direction, carrot stems and leaves produce a rotation angle θ_xz in the xz plane, as shown in Figure 4, and the calculation formula is shown in Formula (4) [17].

$${\theta }_{xz}={\displaystyle \frac{F_x{H}^2 }{2EI}}$$

(4)

Here, θ_xz is angle of turn produced by a carrot stem and leaf in the xz plane, (°); F_x is the forward thrust, N; EI is the bending strength of carrot stems and leaves, GPa.

Formula (5) is derived from the geometric relationship:

$${\theta }_{xz}={\displaystyle \frac{{180}^{\circ }·arctan\left[\left(1000\right(v_1-v_{\omega x}) t/H)\right] }{\pi }}$$

(5)

Here, v₁ is the rotation time for the disc knife to contact the stalk and start cutting, m/s; v_ωx is the disc knife rotation line speed along the forward direction velocity, m/s, m/s; t is the rotation time for the disc knife to contact the stalk and start cutting, s.

v_ωx is calculated by Formula (6):

$$v_{\omega x}={\displaystyle \frac{2\pi n{r}_k\cos \beta }{1000}}$$

(6)

Here, n is the rotational speed of the disc cutter, r/min.

This is, thus, obtained according to Formula (7):

$$F_x={\displaystyle \frac{2EI\cdot {180}^{\circ }\arctan (1000\Delta v_{x}t/H) }{\pi H^2}}$$

(7)

Formula (10) can be obtained from the above equation [17]:

$$F_x={\displaystyle \frac{2EI\cdot {180}^{\circ }\arctan \left[(1000v_1-\pi n{r}_k\cos \phi /30)t/H\right] }{\pi H^2}}$$

(8)

When the forward thrust exceeds the bending force limit of the stem and leaf during the contact process, the stem and leaf produce a tilt that affects the cutting effect. From Formula (8), it can be seen that the forward thrust of the carrot stem and leaf is positively correlated with the forward speed and negatively correlated with the rotational speed of the cutter, and the forward speed and the rotational speed of the cutter are the key motion parameters affecting the cutting operation parameters.

2.2.3. Disc Knife Structure Design

The disc knife structure has an important effect on the cutting resistance, which is related to the shape of the cutting edge of the cutting operation and the effective arc length of the cutting edge operation by the theorem of the test constants of Golichkin’s mechanics. In order to increase the effective arc length and reduce the cutting resistance, a wavy disc cutter is designed in this study. In this study, the commonly used light-edged disc cutter, serrated disc cutter and the wavy disc cutter designed in this study were selected for the comparative test of carrot harvesting performance. The radius of the three disc cutters was 95 mm, the thickness of the base was 3 mm, the inclination angle of the disc cutter blade was 17.1°, and all of them were made of high-speed steel; among them, the number of teeth in the serrated disc cutter was 48, and the structure of the disc is as shown in Figure 5b.

As shown in Figure 5a, the edge-shaped disc knife in the cutting process by the reaction force for the cutting pressure to the slip-cutting-based cutting process is smooth, and the cutting resistance is small. For the serrated disc knife shown in Figure 5b, the knife in the cutting process by the reaction force is mainly cutting tension; serrated teeth can hook carrot stems and leaves constantly sawing and the clamping ability of the stems and leaves is strong, but cutting the cutting teeth of the cutting impact caused by the cutting resistance is larger. For the wavy disc knife shown in Figure 5c, the knife effective edge length is longer, the cutter and the stem and leaf contact area is small, and the friction resistance is smaller; the cutting process there is a slide cut and chopping role and can effectively reduce the cutting resistance. From the above analysis, it can be seen that the structure of the knife disc has a greater impact on the cutting effect, so the light edge, serrated and wave-shaped structures of the knife disc are used for a comparison test.

Because the light-edged disc cutter and serrated disc cutter are used more in the field of agricultural engineering, they are not parameterized; while the wavy disc cutter is used less, based on the physical properties of carrot stems and leaves, the structural parameters of the wavy disc cutter edge need to be designed. In order to determine the structural parameters of the wavy disc knife, its slip angle is calculated, according to the two-point distance calculation formula in the polar coordinate system (such as Figure 5c). The trajectory of the outer end point of the wavy disc cutter should conform to Formula (9) [18]:

$${\rho }^2-2\rho {\rho }_0\cos (\theta -{\theta }_0)+{{\rho }_0}^2=r^2$$

(9)

Here, ρ is the polar diameter; ρ₀ is the polar diameter at the center of the arc, mm; θ₀ is the polar angle at the center of the arc (°); r is the radius of the wave arc, mm; θ is the polar angle when the polar diameter is ρ (°); and α is the slip tangent angle (°).

Meanwhile, Formula (10) can be obtained based on the related geometric relationship [15]:

$$\alpha =\arctan {\displaystyle \frac{\sqrt{r^2-{\rho }_0{\sin }^2(\theta -{\theta }_0)}}{r^2-{\sin }^2(\theta -{\theta }_0)}}$$

(10)

Because the maximum cutting resistance point is after the cutter disc contacts the stem and leaves, according to the geometrical relationship, the extreme angle θ = 39.96° is calculated at this point. The smaller the arc radius, the smaller the slip angle, but if the arc radius is too small, the high processing costs and friction resistance increase. The slip angle of 20–55° for a reduction in cutting power consumption is favorable in the actual situation. The slip angle of 39.75°, according to the Formula (10), determines the arc radius of 12 mm, the polar coordinates of the center of the arc circle (75 mm, 45°), combined with the pre-test situation, and ultimately determines the cutter disc circumference of the arrangement of the 18 sections of the arc edge curve.

Among the above three structural disc cutters, the wave-type disc cutter was finally selected in this study, mainly for two reasons: one is due to the fact that there is more research related to the light-edged disc cutter and the serrated disc cutter, and there is less research on the wave-type disc cutter in the field of carrot harvesting; the second reason is from the structural aspect, as, due to the fact that the contact area between the blade of the wave-type disc cutter and the material is intermittent, it saves relative effort when cutting. Therefore, the wave-type disc cutter was finally selected in this study, and it was mounted on a double-disc cutter cutting device for testing.

2.3. Test Condition

The experiment was carried out in May 2024 in Xuzhou City, Jiangsu Province. The test carrot variety is ‘Sanhong’, the test plot area is 11,000 m², the soil type is sandy loam, the soil water content at a depth of 0–100 mm is 21.25%, the soil firmness is 1.1 MPa, the soil capacity is 1.2 g/cm³. 1.1 MPa, and the soil bulk density is 1.2 g/cm³. Figure 6 shows the test scene. The variety was standardized and sown in February; then, effective fertilizer, water supply and growth observations were carried out during the growing period, integrated pest and weed control was carried out, and the test plot with consistent growth was selected in June of each year for a hanging trial to collect relevant data. Thus, 16,000 plants were planted. The experiment was carried out on the mobile test bench from Section 2.1, and the disc cutter cutting device was hung behind the clamping and conveying device. Other auxiliary tools are electronic scales (made by China Shanghai Lichen Instrument Technology Co., Ltd., Shanghai, China, model: YP300001D, range 0–30 kg, accuracy 0.0001 kg), Vernier caliper, tape measure (0–150,000 mm), stopwatch, and other equipment.

2.4. Evaluation Criteria and Calculation Method

From the literature and market survey, it can be seen that the length of carrot stems and leaves remaining after cutting is greater than 30 mm, which will lead to accelerated carrot decay and is not conducive to the storage and transport of carrots; whether or not the carrot rhizome is damaged and whether or not the stem and leaf cutting is neat are the main factors in determining the economic value of carrots. Therefore, the carrot root damage rate, stem and leaf cutting rate and cutting surface flatness rate were selected as test indicators. The detailed definition of each test index of unsatisfied carrots is shown in

Table 2. Methods of post-harvest evaluation and judgement of carrots.

Results	Evaluation and Judgement Methods	Schematic Diagram
Pass	Pass Size	Figure 6a
Root and stem damage rate	Carrot stems and fruits are damaged if the epidermis is detached and the flesh tissue is broken	Figure 6b
Stem and leaf cutting rate	For the convenience of statistics, the length of carrot stem and leaves remaining after cutting is greater than 40 mm, which is regarded as unclean stem and leaves cutting	Figure 6c
Flatness of cut surface	Deducting the stem and leaf cuttings, the unevenness of the cutting surface is considered as uneven cutting	Figure 6d

and Figure 7.

During the test, the carrots whose stems and leaves were cut were collected and counted in total, and the number of carrots with root and stem damage, clean cut stems and leaves and flat cutting surface were picked and counted. Formula (11) is used to calculate these three indicators:

$$\left\{\begin{array}{l}G={\displaystyle \frac{W_1}{W}}\times 100\%\\ Q={\displaystyle \frac{W_2}{W}}\times 100\%\\ Z={\displaystyle \frac{W_3}{W}}\times 100\%\end{array}\right.$$

(11)

Here, G is the damage rate, %; Q is the stem and leaf clearance, %; Z is the cutting surface flatness, %; W₁ is the weight of carrots with root damage, %; W₂ is the weight of carrots with clean stem and leaf cuts, %; W₃ is the cutting surface levelling carrots, %; and W is the mass of all harvested carrots, g.

2.5. Experimental Program Design

Based on the previous single-factor test data, the selection range of the two working parameter factor levels affecting the working performance of the double-disc knife-cutting device was determined. On this basis, in order to obtain the optimal working parameter combination of the double-disc knife-cutting device, a multifactorial test was conducted with the clamping conveyor speed and disc knife rotational speed as the test factors and the carrot root and stem damage rate, the stem and leaf cutting clean rate and the cutting surface flatness rate as the test indexes [19,20].

In order to investigate the optimal working parameters of the double-disc knife-cutting device, the clamping and conveying speed x₁, disc knife speed x₂, and disc knife thickness x₃ were selected as the test factors on the basis of the previous single-factor test and theoretical analysis. In the field test, the mobile test bed is equipped with an automatic control function, which can realize the constant speed cruise test and keep the forward speed at 0.8 m/s. The test took the root damage rate Y₁, the stem and leaf cutting net rate Y₂, and the cutting surface flatness rate Y₃ as the indexes and carried out a three-factor, three-level orthogonal test. The test factors and levels are shown in

Table 3. Factors and levels of experiment.

Level	Factors
	Clamping and Conveying Speed x1/(m/s)	Rotational Speed of Disc Cutter x2/(r/min)	Thickness of Disc Cutter x3/(mm)
1	0.65	150	2
2	1.05	180	4
3	1.45	210	6

.

The experiment is designed according to the principle of the Box–Behnken test. The Box–Behnken test is an experimental design method based on the response surface method (RSM), which is mainly used to optimize the relationship between multiple continuous variables (factors) and response variables. Its core principle is to find the optimal process conditions or parameter combinations by reasonably arranging experimental points, constructing polynomial models and analyzing the main effect, interaction effect and secondary effect of factors. During the experiment, each factor takes three levels: low (−1), medium (0) and high (+1). All factors take the middle level, which is used to estimate the experimental error and model curvature. The core advantage of this method is that it balances the number of experiments and the complexity of the model, and it is suitable for the optimization of the number of medium factors. According to this principle, 17 experimental points are arranged in the experiment. The experimental design scheme is shown in

Table 4. Experimental design program.

No.	Factors
	Clamping and Conveying Speed x1/(m/s)	Rotational Speed of Disc Cutter x2/(r/min)	Thickness of Disc Cutter x3/(mm)
1	0	1	−1
2	0	1	1
3	1	0	−1
4	−1	1	0
5	0	−1	1
6	−1	0	1
7	1	0	1
8	1	1	0
9	0	0	0
10	0	0	0
11	0	−1	−1
12	0	0	0
13	−1	0	−1
14	1	−1	0
15	−1	−1	0
16	0	0	0
17	0	0	0

, and the statistical analysis software was applied to the test.

Design-Expert 8.0.6 is used to process and analyze the test results and establish the mathematical model between the test parameters and performance indicators. The ANOVA model is used with the quadratic model. After all the experimental data were collected, we finally carried out the quadratic polynomial regression analysis on the root and stem damage rate Y₁, stem and leaf cutting net rate and cutting surface levelling rate and used the response surface analysis method to analyze the correlation and interaction effects of the various factors. Correlation and interaction effects were analyzed and studied. In order to avoid missing cutting, the cutting height h of the cutter is 150 mm, and the bending modulus of the stem and leaf where the carrot is cut is measured according to the mechanical characteristics test. The minimum working speed (forward speed) of the test bench is determined to be 0.85 m/s. The highest working speed of the test bed is 1.60 m/s. Therefore, considering the quality and efficiency of the test bed, the range of test clamping and conveying speed is determined to be 0.65–1.45 m/s. Double-disc cutting belongs to low-speed supported cutting. Combined with previous experiments, the minimum rotation speed of the disc cutter is designed to be 150 r/min. Combined with the actual test conditions, the highest rotating speed of the disc cutter is designed to be 240 r/min. According to the previous test, the rotating speed range of the test cutter head is 160–240 r/min. According to the research of Kong [21], the cutter head thickness is also an important factor affecting the cutting ability. According to the previous test, the cutter head thickness range is 2–6 mm.

3. Results

3.1. Results and Analyses of Multifactorial Tests

In the course of the test, the Box–Behnken test program was kept consistent with the coding table of the test factor levels, and the measured data were statistically calculated and averaged as the test results, which were collated and filled in the table, as shown in

Table 5. Experimental design scheme.

No.	Clamping and Conveying Speed x1/(m/s)	Rotational Speed of Disc Cutter x2/(r/min)	Thickness of Disc Cutter x3/(mm)	Root and Stem Damage Rate Y1/%	Performance Indicators Stem and Leaf Cutting Rate Y2/%	Cutting Surface Flatness Rate Y3/%
1	0	1	−1	4.52	92.22	79.25
2	0	1	1	5.13	87.13	69.70
3	1	0	−1	4.21	84.11	76.14
4	−1	1	0	3.72	95.27	81.23
5	0	−1	1	4.76	78.98	72.30
6	−1	0	1	4.56	76.33	73.30
7	1	0	1	4.83	70.65	66.64
8	1	1	0	4.03	89.94	75.20
9	0	0	0	2.51	88.34	90.19
10	0	0	0	2.62	89.13	91.39
11	0	−1	−1	4.12	80.67	82.11
12	0	0	0	2.56	88.98	90.82
13	−1	0	−1	3.91	81.32	83.12
14	1	−1	0	3.62	76.25	78.62
15	−1	−1	0	3.36	83.88	85.54
16	0	0	0	2.63	88.96	92.69
17	0	0	0	2.57	87.25	91.83

.

(1)

Analysis of the effect of factors on the damage rate of carrot rootstock.

For experimental data processing and analysis using the statistical analysis software Design-Expert 8.0.6, the three factors on the carrot root damage rate of the variance of the analysis screened out the more significant factors and the factors on the root damage rate of the analysis of variance, as shown in

Table 6. Analysis of variance (ANOVA) of factors on the rate of rhizome damage.

Source	Root and Stem Damage Rate Y1
	Sum of Squares	Degrees of Freedom	F	p
Model	12.83	9	1047.08	<0.0001
x1x1	0.1625	1	119.32	<0.0001
x2x2	0.2965	1	217.75	<0.0001
x3x3	0.7938	1	583.06	<0.0001
x1x2	0.0006	1	0.4591	0.5198
x1x3	0.0002	1	0.1653	0.6965
x2x3	0.0002	1	0.1653	0.6965
x12	0.7596	1	557.97	<0.0001
x22	1.95	1	1429.03	<0.0001
x32	7.96	1	5845.06	<0.0001
Residual	0.0095	7
Mismatch	0.0001	3	0.0070	0.9991
Error checking	0.0095	4
Sum	12.84	16

.

Multiple regression fitting analysis was carried out on the data in Table 6 using Design-Expert software to establish the response surface regression model of Y₁ on x₁, x₂ and x₃, and the regression formula (Formula (12)) was subjected to analysis of variance, as shown in Table 6. The response surface regression model of Y₁ on x₁, x₂ and x₃ was:

$$Y_1=2.58+0.14x_1+0.19x_2+0.32x_3+0.01x_1{x}_2-0.0075x_1{x}_3-0.0075x_2{x}_3+0.42{x_1}^2+0.68{x_2}^2+1.37{x_3}^2$$

(12)

Here, Y₁ is root damage rate, %; x₁ is the clamping conveyor speed, m/s; x₂ is the rotational speed of disc cutter, r/min; x₃ is the thickness of the disc cutter, mm.

As can be seen in Table 6, the p-values of the Y₁ model for the root damage rate were all less than 0.05, indicating that the model impact was highly significant. And the coefficient of determination R² value is 0.9993, indicating that more than 99% of the response value can be explained by this model. The p-value of the misfit term is greater than 0.05, and the misfit is not significant, indicating that the model fit is high; therefore, the model can predict the working parameters of the double-disc knife-cutting device. According to the magnitude of the regression coefficients of each factor of the two models, the main order of influence of each factor on the damage rate of rhizomes can be obtained as x₃, x₂, x₁, clamping and conveying speed, rotational speed of the disc knife, and thickness of the disc knife.

Figure 8 shows the response surface of the influence of each factor on the damage rate of the carrot rhizome. From Figure 8a, when the rotational speed of the disc knife is certain, the damage rate of the rhizome gradually decreases with an increase in the clamping and conveying speed; the reason is that the larger the clamping and conveying speed, the easier it is to cut the carrot tassel intact, and the jittery nature of this cutting process is small. The cutting is rapid in the process of cutting, resulting in damage to the carrot rhizome caused by rhizomes and the cutting device. When the clamping and conveying speed is certain, the damage rate of the rhizome rises with an increase in the rotational speed of the disc knife and then gradually decreases. In the cutting process, the cause of carrot root damage is the collision between the root and the cutting device. The larger the clamping conveying speed and the rotational speed of the disc cutter, the shorter the time of carrot conveying and cutting; the shorter the time of collision with the device, the smaller the root damage rate. As can be seen in Figure 8b, when the clamping and conveying speed is certain, the root damage rate with an increase in the thickness of the disc cutter shows a gradual decrease in at first and then a rapid increase in the change trend. When the thickness of the disc cutter is certain, the root damage rate with a reduction in the rotational speed of the disc cutter is gradually reduced, with a rapid increase in the first; the reason is that, for the disc cutter thickness of the interval for 1–2 mm, with the increase in the thickness of the cutting instant, the stem fiber deformation is greater and greater, and the overall contact area is greater and greater. The reason is that when the thickness of the disc knife is 1–2 mm, the cutting instant and the degree of deformation of the stem and leaf fiber are bigger and bigger, the overall contact area is bigger and bigger, and its maximum cutting force increases more and more, which is more conducive to smooth cutting. Therefore, the damage rate of the carrot root and stem decreases gradually, and when the thickness of the disc knife is more than 2 mm, the greater the thickness. In addition to cutting, the cutting force of the stem and leaf fiber, the stem and leaf fiber and plastic deformation caused by the friction of the knife disc are larger, resulting in a decline in the cutting performance and an increase in jittering, which would increase the damage rate of the carrot root and stem. From Figure 8c, it can be seen that when the thickness of the disc knife is certain, the disc knife speed interval is located at 160–200 r/min, and the root damage rate with an increase in the disc knife speed shows a gradual decrease first, because, with an increase in the rotational speed of the disc knife, the kinetic energy of the disc knife cutting continues to increase, and the cutting becomes smoother, but the disc knife speed interval is located at 160–200 r/min. However, when the rotational speed range of the disc knife is 160–200 r/min, the damage rate of the carrot root and stem increases, which is due to the larger sliding angle of the disc knife. Too large a sliding angle of cutting can easily produce slippage; at this time, the knife blade cannot clamp the stems and leaves, and the carrot stems and leaves are easy to push out of the stems and leaves for bending, resulting in an increase in the rate of loss of cutting.

(2)

Analysis of the effect of various factors on stem and leaf cutting efficiency.

The statistical analysis software used for processing and analyzing the experimental data was Design-Expert 8.0.6, and

Table 7. Analysis of variance (ANOVA) for stem and leaf cuttings.

Source	Stem and Leaf Clearance Y2
	Sum of Squares	Degrees of Freedom	F	p
Model	597.04	9	12.99	0.0014
x1x1	31.40	1	6.15	0.0422
x2x2	46.18	1	9.04	0.0197
x3x3	79.57	1	15.58	0.0055
x1x2	1.32	1	0.2590	0.6264
x1x3	17.94	1	3.51	0.1030
x2x3	2.89	1	0.5660	0.4764
x12	82.34	1	16.13	0.0051
x22	140.41	1	27.50	0.0012
x32	151.95	1	29.76	0.0010
Residual	35.74	7
Mismatch	33.32	3	18.34	0.0084
Error checking	2.42	4
Sum	632.78	16

shows the analysis of variance (ANOVA) of the factors on the stem and leaf cutting rate of carrots.

Multiple regression fitting analysis was carried out on the data in Table 7 using Design-Expert software, and Formula (13) was used to express the response surface regression model of Y₂ on x₁, x₂, and x₃:

$$Y_2=88.53-1.98x_1-2.4x_2-3.15x_3+0.58x_1{x}_2-2.12x_1{x}_3-0.85x_2{x}_3-4.42{x_1}^2-5.57{x_2}^2-6.01{x_3}^2$$

(13)

Here, Y₂ is the stem and leaf clearance, %.

As can be seen from Table 7, the p-values of the stem and leaf cutting net rate Y₂ were all less than 0.05, indicating that the model impact was highly significant. And the coefficient of determination R² values were 0.9435, indicating that more than 94% of the response value can be explained by this model. The p-values of the misfit term are greater than 0.05, and the misfit is not significant, indicating that the model fit is high; therefore, the model can predict the working parameters of the double-disc knife-cutting device. According to the size of the regression coefficient of each factor in the model, we can obtain the primary and secondary order of the influence of each factor on the stem and leaf cutting net rate as x₃, x₂, x₁, i.e., the clamping and conveying speed, the rotational speed of the disc knife, and the thickness of the disc knife. The primary and secondary order of the influence of each factor on the stem and leaf cutting net rate is x₃, x₂, x₁, i.e., the thickness of the disc knife, the rotational speed of the disc knife, and the clamping and conveying speed.

Figure 9 shows the response surface of the influence of each factor on the carrot stem and leaf cutting rate. From Figure 9a, it can be seen that when the conveying speed is certain, the stem and leaf cutting rate increases with an increase in the rotational speed of the disc cutter, because, with an increase in the rotational speed of the disc cutter, the kinetic energy of the disc cutter increases, the cutting becomes smoother, and the stem and leaf cutting rate increases. When the rotational speed of the disc knife is certain, the stem and leaf cutting net rate with an increase in the delivery speed shows a trend of first increasing and gradually decreasing, because when the delivery speed is faster, the carrot stem and leaf through the cutting area of the time arr shorter, and some of the stem and leaf are not cut in time, resulting in a decline in the stem and leaf cutting net rate. As can be seen from Figure 9b, when the clamping conveying speed is certain, the stem and leaf cutting net rate with an increase in the thickness of the disc cutter shows an increase in the first after the decrease in the change trend; when the thickness of the disc cutter is certain, the stem and leaf cutting net rate with a reduction in the rotational speed of the disc cutter is first gradually reduced and then increased rapidly. The reason for this is that the thickness of the disc cutter is smaller. With an increase in the thickness of the cutter, the stem and leaf fiber deformation and the overall contact area become larger. The maximum cutting force becomes larger, and it has maximum cutting force.

As can be seen in Figure 10c, when the thickness of the disc knife is certain, the stem and leaf netting rate increases gradually with an increase in the disc knife speed, which is because, with an increase in the disc knife speed, the kinetic energy of the disc knife cutting continues to increase, the cutting becomes smoother, and the stem and leaf netting rate increases continuously. However, when the rotational speed of the disc knife exceeds a certain value, because the disc slip cutting angle is large and can easily produce slip, at this time, the knife blade cannot clamp the stem and leaves, meaning that the carrot stem and leaves can easily be pushed out of the stem and leaf bending, resulting in a decline in the rate of stem and leaf cutting.

(3)

Analysis of the effect of factors on the cutting surface flatness rate.

For the experimental data processing and analysis using the statistical analysis software Design-Expert 8.0.6, the three factors on the cutting surface flatness rate of the variance of the analysis screened out the more significant factors, and the factors on the cutting surface flatness rate of the analysis of variance are shown in

Table 8. Analysis of variance (ANOVA) for cutting surface flatness rate.

Source	Cutting Surface Flatness Rate Y3
	Sum of Squares	Degrees of Freedom	F	p
Model	88.38	9	196.43	<0.0001
x1x1	21.75	1	142.15	<0.0001
x2x2	187.02	1	34.98	0.0006
x3x3	0.1980	1	300.80	<0.0001
x1x2	0.0256	1	0.3185	0.5901
x1x3	0.0169	1	0.0412	0.8450
x2x3	158.64	1	0.0272	0.8737
x12	109.44	1	255.16	<0.0001
x22	459.43	1	176.02	<0.0001
x32	88.38	1	738.94	<0.0001
Residual	4.35	7
Mismatch	0.7038	3	0.2572	0.8532
Error checking	3.65	4
Sum	1103.49	16

.

Multiple regression fitting analyses were carried out on the data in Table 8 using design-Expert 8.0.6, and Formula (14) was used to calculate the response surface regression model of Y₃ on x₁, x₂, and x₃.

$$Y_3=91.38-3.32x_1-1.65x_2-4.84x_3+0.22x_1{x}_2+0.08x_1{x}_3+0.065x_2{x}_3-6.14{x_1}^2-5.10{x_2}^2-10.45{x_3}^2$$

(14)

Here, Y₃ is the cutting surface flatness rate, %.

As can be seen from Table 8, the p-value of the cutting surface flatness Y3 is less than 0.05, indicating that the model impact is highly significant. And the R2 value of the coefficient of determination is 0.9344, indicating that more than 93% of the response value can be explained by this model. The p-value of the misfit term is greater than 0.05, and the misfit is not significant, indicating that the model fit is high; therefore, the model can predict the working parameters of the double-disc knife-cutting device. According to the size of the regression coefficients of each factor of the two models, the main order of influence of each factor on the flatness of the cutting surface is x₃, x₁, x₂, i.e., the thickness of the disc knife, the clamping and conveying speed, and the speed of the disc knife.

Figure 10 illustrates the response surface analysis results for each operational parameter affecting the cutting surface flatness rate. Figure 9a demonstrates the interactive effect between the clamping–conveying speed and disc cutter rotational speed. As both parameters increase, the flatness rate initially rises and then gradually declines. This trend mirrors the observation in Figure 8a, indicating consistent performance patterns across different experimental configurations.

In Figure 10b, two distinct relationships emerge. When the clamping–conveying speed is held constant, increasing disc knife thickness causes the flatness rate to first increase and then decrease. Conversely, at a fixed knife thickness, reducing the clamping–conveying speed leads to an initial gradual decrease followed by a rapid increase in flatness. These phenomena require mechanistic interpretation.

For thinner disc knives, increasing thickness enhances the cutting moment, leading to progressive stem–leaf fiber deformation. The expanding contact area between the blade and material increases the maximum cutting force, which promotes smoother cutting and improves flatness. However, when thickness exceeds the optimal value, excessive material engagement introduces additional friction forces. This friction induces the elasto-plastic deformation of plant tissues, causing operational instability. The resultant cutting jitter negatively impacts surface quality, leading to a flatness rate reduction.

These results highlight the dual role of disc knife thickness: while moderate increases improve cutting efficiency through enhanced force transmission, excessive thickness introduces destabilizing frictional effects. The optimal thickness lies at the equilibrium point between these competing mechanisms, balancing cutting force and process stability. As can be seen in Figure 10c, when the thickness of the disc knife is certain, the rotational speed of the disc knife is small and the cutting surface flat rate increases with an increase in the rotational speed of the disc knife, because the rotational speed of the disc knife is small. With an increase in the rotational speed of the disc knife, the kinetic energy of the disc knife cutting increases, the cutting becomes smoother, and the cutting surface flat rate is increasing, but when the rotational speed of the disc knife is more than a certain value, due to the disc sliding angle being larger, it is easy to produce slip and, at this time, the knife blade cannot easily produce slip. At this time, the knife blade cannot clamp the stem and leaves, and the carrot stem and leaves are easy to push out of the stem and leaf bending, resulting in a decline in the cutting surface flatness.

3.2. Test Optimization and Validation

Based on the analysis of the above test results, in order to further improve the operational performance of the double-disc knife-cutting device, under the level constraints of the test factors, the minimum value of rhizome damage rate Y₁, the maximum value of stem and leaf cleaning rate Y₂ and the maximum value of cutting surface flatness rate Y₃ are taken as optimization indexes, and the full-factor quadratic regression Formula (15) of the performance indexes is established to carry out the target optimization and the optimal working parameter determination.

$$\left\{\begin{array}{l}\min Y_1\left(x_1,x_2,x_3\right)\\ \max Y_2\left(x_1,x_2,x_3\right)\\ \max Y_3\left(x_1,x_2,x_3\right)\\ 0.65 \mathrm{m}/\mathrm{s}\le x_1\le 1.45 \mathrm{m}/\mathrm{s}\\ 150 \mathrm{r}/\min \le x_2\le 210 \mathrm{r}/\min \\ 2 \mathrm{m}\mathrm{m}\le x_3\le 6 \mathrm{m}\mathrm{m}\end{array}\right.$$

(15)

The constraint optimization solving module in Design-Expert software was employed to identify optimal parameter combinations. Two key objectives were considered: minimizing the root and stem damage rate (Y₁) and maximizing the stem and leaf cutting rate (Y₂). The resulting solution yielded specific parameter values. One optimal working parameter combination was selected through comprehensive analysis. This combination included a carrot clamping and conveying speed of 0.95 m/s, a disc knife rotational speed of 193.34 r/min, and a disc knife thickness of 3.67 mm. Under these conditions, the double-disc knife-cutting device achieved optimal performance. The corresponding root damage rate was 2.54%, the stem and leaf cutting net rate reached 89.26%, and the cutting surface flatness rate was 92%.

The practical implementation of theoretically optimized parameters faced challenges due to mechanical adjustment limitations. To address this, a parameter set close to the optimized values was chosen for field verification. The adjusted parameters included a clamping and conveying speed of 1.0 m/s, a disc cutter rotational speed of 193.5 r/min, and a disc cutter thickness of 3.6 mm. The field tests were conducted in 2024 at the original experimental site using identical methods. Each test was repeated three times, and the results were averaged. The validated outcomes showed a root and stem damage rate of 2.61%, a stem and leaf cutting rate of 87.32%, and a cutting surface flatness of 89.87%. These values closely matched the theoretical optimization results. Furthermore, the cutting performance exceeded that of existing carrot double-disc knife-cutting devices.

A comparative analysis was conducted under identical operational conditions using commonly adopted parameters for carrot harvesting devices. The optimized system demonstrated significant improvements. Specifically, the root and stem damage rate decreased by 2.16 percentage points. The stem and leaf cutting net rate improved by 1.97 percentage points. Productivity also increased by 1.87 percentage points compared to pre-optimization levels. These results collectively indicate a substantial enhancement in overall performance.

4. Discussion

Carrot clamping and extraction operations are emerging as a critical harvesting method in China. This mode directly impacts or even determines three key performance metrics: the rhizome damage rate, stem and leaf cutting net rate, and cutting surface levelling rate. Understanding these relationships is essential for optimizing harvesting efficiency. This study investigates how different clamping and conveying devices affect rhizome damage. It also evaluates stem/leaf cutting net rates and cutting surface quality under varying operational conditions. Specifically, experiments compare responses across distinct carrot varieties and clamping speeds. Analyzing these parameters offers both theoretical and practical benefits. Improved operational performance of the harvesting implements is a primary goal. This includes selecting optimal clamping devices tailored to specific carrot varieties. Additionally, identifying the most suitable clamping and conveying speeds is critical. Enhancing double-disc cutting devices for carrots remains a priority. Reducing root and stem damage rates is a key objective. Simultaneously, increasing stem/leaf cutting net rates and cutting surface levelling efficiency is essential. Achieving these improvements will elevate the overall harvesting quality. The rhizome damage rate reflects mechanical stress during clamping. The stem/leaf cutting net rate measures the successful removal of non-edible parts. The cutting surface levelling rate quantifies post-cutting smoothness. These metrics collectively define the harvesting device performance. Systematic testing across multiple carrot varieties is proposed. Variable clamping speeds will be applied to identify optimal ranges. Comparative evaluations between different clamping systems will inform technology upgrades. Data-driven improvements aim to reduce post-harvest losses.

Zeng (2023) [10] used the Box–Behnken test method to design a three-factor, three-level test to establish a regression mathematical model for each factor and the success rate of carrot rhizome separation and carrot damage rate. The results showed that the parameters of the carrot rhizome separation mechanism had a significant effect on the effect of rhizome separation, and, at the same time, the optimal parameters of the carrot rhizome separation mechanism were obtained. Under the optimized working parameters, the success rate of carrot rhizome separation was 96.2%, and the damage rate of the carrot was 5.2%, which corresponded to the damage rate of the rhizome after the test bench test was 2.61%. The damage rate of the rhizome in this study was significantly superior to the results of the two others from this study.

The structures of the double-disc cutting device researched by Zhao (2023) [22] and the double-disc cutting device in this study are very similar, so the two are highly comparable. From the experimental results, the test bench in this study corresponds to a carrot rhizome damage rate of 1.67%, a stem and leaf cutting rate of 95.41%, and a cutting surface flatness rate of 75.22%, whereas the clamping and conveying speed in this study is 1.0 m/s, the disc knife speed is 193.2%, and the root damage rate is 2.61%. Compared with these two results, this study is significantly better than the previous study. When the rotational speed of the disc knife is 193.5 r/min, and the thickness of the disc knife is 3.6 mm, the corresponding root damage rate is 2.61%, the stem and leaf netting rate is 87.32%, and the cutting surface levelling rate is 89.87%. Comparing these two results, the root damage rate and stem and leaf netting rate in this study are better than that of the previous study, but from the point of view of the cutting surface levelling rate, the results of this study are higher than that of the previous study by 14.65 percentage points, which also proves the scientific and advanced nature of this study to a certain extent.

Yao et al. (2023) [23] conducted a field test on the damage rate of white radish, and the test results showed that the whole machine had stable operational performance, and the damage rate was less than 2.7%. Although white radish is different from the carrot studied in this paper, the operation principle of this white radish combine harvester is different, and the appearance characteristics and planting characteristics of white radish and the carrot studied in this paper are extremely similar; the damage rate of the carrot rhizomes corresponding to this study’s test stand was 1.67%, and the damage rate the test stand was 1.67%. The rate was 1.67%, and the experimental results were significantly better than those of Yao et al. (2023) [23]. Although white radish differs from the carrot studied here, their harvesting principles vary. Despite this, white radish shares striking similarities with carrots in terms of appearance and planting characteristics. These resemblances further validate the findings of Yao et al. (2023) [23]. The results presented here, thus, reinforce the accuracy of their research.

This study achieved certain experimental innovations; however, there are some limitations, as follows:

Due to the subjective and objective factors such as time and conditions, this study carried out experiments by setting up a multifactorial test method, analyzed the root and stem damage rate, stem and leaf cutting net rate and cutting surface flatness rate of a single variety of carrots, focusing on the macroscopic point of view, and did not conduct an in-depth study on the characteristics and laws of the movement of the carrot plant and carrots in the disc cutter cutting device. Combining the automation control and intelligent monitoring technology, we will design a new system for carrots with the help of the automation control and intelligent monitoring technology in the next step. The next step is to design a synchronous monitoring and adjustment system with the top cutting device by combining automation control and intelligent monitoring technology and to improve the cutting quality through intelligent control technology, such as installing a rotational speed intelligent adjustment system on the disc cutter, which can intelligently adjust the rotational speed of the disc cutter according to the travelling speed of the machine in the field in order to improve the operational efficiency.

Through the results of this study, it can be found that when designing a carrot combine, the thickness and rotation speed of the selected disc cutter and the working parameters of the disc cutting device and the clamping and conveying device should be considered in coordination, and the optimal parameter interval has a great correlation with the clamping and conveying speed and carrot varieties (the physical dimensions of different varieties of stem and leaves and carrot stalks are often quite different). At the same time, automatic speed control technology is needed to control the rotation speed of the disc cutter and the forward speed of the machine.

5. Conclusions

In this study, the optimum operating parameters of the double-disc cutter are determined, and the designed double-disc cutter is used as the research carrier to build a double-disc cutter test rig for indoor bench tests to carry out single-factor and multi-factor performance optimization tests for the double-disc cutter, obtain the optimum combination of the operating parameters of the double-disc cutter, and validate the superiority of the double-disc cutter. The specific conclusions are as follows:

(1) Based on geometric relations, the polar angle is θ = 39.96, sliding angle is 20°–55°, arc radius is 12 mm, and arc center polar coordinates are 75 mm, 45. Integrating prior test data, 18 arc cutting edge curves are finalized.

(2) Comparative analysis of the three disc structures (light-edge, serrated, wavy) resulted in selecting the wavy configuration as the cutting implement to prevent material leakage (cutting height H = 150 mm). The carrot stem/leaf bending modulus was determined via experiments and established the minimum test bench speed. The forward speed limits were 0.85 m/s (lower) and 1.60 m/s (maximum). System constraints necessitated parameter balancing prioritizing quality/efficiency, yielding a clamping/conveying speed range of 0.65–1.45 m/s. The design parameters derived from a prior experimental dataset showed a minimum disc cutter speed of 150 r/min, while the actual test conditions adjusted the operational speed range to 160–240 r/mi.

(3) The Box–Behnken design was applied to optimize the operational parameters of a double-disc knife-cutting device. A regression model describing the cutting performance relationships was constructed via systematic experiments and validated using Design-Expert 8.0.6 software.

Field trials were conducted in 2024 at 1.0 m/s clamping conveyor speed, 193.5 r/min disc cutter rotation, and 3.6 mm disc thickness (triplicated under standardized conditions) and yielded 2.61% carrot root/stem damage, 87.32% stem/leaf netting efficiency, and 89.87% cutting surface flatness.

Comparative analysis with pre-optimization parameters demonstrated significant improvements: 2.16% reduction in root/stem damage, 1.97% improvement in stem/leaf netting efficiency, and 1.87% productivity enhancement.

(4) All comparisons were conducted under identical experimental conditions. Statistical analysis confirmed the performance enhancements. Optimized parameters demonstrated superior operational efficiency. The systematic approach validated the predictive capability of the mathematical model. Controlled experimentation quantitatively demonstrated technical improvements.