Experimental Research on the Effect of Sugarcane Stalk Lifting Height on the Cutting Breakage Mechanism Based on the Sugarcane Lifting–Cutting System (SLS)

Abstract

The sugarcane lifting–cutting System (SLS) is the core component of the sugarcane harvester, and the influence of its stalk lifting height on the mechanism of perennial root-cutting damage is still unclear. The test was conducted with the vertical height of centroid (VHC), forward velocity, and cutter rotational speed. Numerical quantification of perennial root based on the cutting breakage effect and cutting breakage grade (CBG) classification was used as the evaluation index. The test results showed that the VHC had a highly significant effect on the CBG of the perennial root. The CBG of the stalk decreased significantly with the lifting height. The average CBG was greater than 2.0 when the stalk lifting height was severely collapsed. The CBG ≤ 1.6 was considered qualified, and the requirements were met when the VHC of the stalk was about 0.85~1.0 m at a forward velocity of 1~3 km/h. The inverted angle of the stalk being lifted was selected to be 45° as the evaluation standard to measure the qualified lifting of the spiral sugarcane lifter. This study provides technical support for the optimal design and selection of operating parameters of the sugarcane harvester.

1. Introduction

Sugarcane is a perennial gramineous plant, an essential raw material for sugar production. Sugarcane is mainly planted in tropical and subtropical areas and is a critical economic pillar industry in many countries and regions [1,2,3,4,5]. China’s total sugarcane cultivation area is about 1.5 million hectares, ranking third in the world, mainly concentrated in Guangxi, Yunnan, Hainan, Guangdong, and other places [6,7,8]. The harvesting of sugarcane is the most labor-intensive part of the process. In China, it is still mainly harvested by hand, which is labor-intensive and has low efficiency [9].

Mechanized sugarcane harvesting has the advantages of high efficiency, low harvesting cost, and low labor intensity, which is an inevitable trend for the development of the industry [10,11,12,13,14]. Affected by typhoons and seasonal winds, sugarcane will collapse in varying degrees yearly. This makes it common for the cutter to have a large cutting loss and a high permanent root-breaking rate in the operation process, which directly affects the emergence and growth of sugarcane in the coming year and leads to the reduction of economic benefits of sugarcane [15,16,17,18,19]. At present, the double-disc cutter is mainly used for cutting sugarcane stalks. Its composition and working principle are shown in Figure 1. The hydraulic motor drives the cutting blade on the double-disc to rotate at high speed to cut off the sugarcane’s root. The stalk is transported to the next stage, with the stubble in the ground.

To reduce the damage of the cutter to the sugarcane stubble, relevant experts have conducted a series of research. Kroes and Harris [20,21] reduced the breakage rate of sugarcane cutting by adjusting parameters such as cutter disc inclination, diameter or cutter disc speed, the number of cutting blades, the cutting radius of the blade, and the distance between cutter disc centers. There are also more extensive studies by scholars on the effects of cutter blade speed, blade edge slip cutting angle, and blade tilt angle on cutting breakage [22,23,24]. Yang et al. [25] conducted an experimental study on the effect of vibration frequency and amplitude on the sugarcane head breakage rate due to the unevenness of the field floor for a single disc cutter. In addition, the simulation of the stalk-cutting process and the variations of cutting force and shear force were also carried out in a series of experiments and analyses using finite element simulation technology [26,27]. The above analysis shows that most of the existing cutter studies have focused on the structural parameters and operating parameters of the cutter discs and blades, reducing the breakage rate of the lodged roots after sugarcane stalk cutting to some extent. In field research, it was found that it was difficult to control the degree of cut and breakage of lodging roots during the mechanized harvesting of sugarcane within a reasonable range. In the case of China, the current rate of persistent root breakage for each type of operation in China is generally as high as 20% or more [28], which is one of the important reasons for the slow promotion process of sugarcane harvest mechanization.

In this paper, the SLS was studied, and its kinematic model was developed. To quantify the degree of root stubble cutting breakage, we ranked the cut breakage level of sugarcane stalk roots as the evaluation index. Different vertical heights of stalk mass, forward velocity, and cutter rotational speed were selected as the test factors and carried out in the experimental study. In addition, the ideal stalk lifting height interval was preferably selected by the cutting breakage level and experimental analysis. The experimental results referenced the sugarcane harvester’s structure optimization and parameter selection.

Existing studies have shown that the cutting breakage for perennial root was carried out using a single cutter, failing to analyze the effect of the lifting height of the stalk on the degree of cutting breakage in conjunction with a lifter. This paper innovatively combines two key components, the sugarcane lifter and the cutter, to carry out relevant experimental research, and adopts a numerical quantification method to evaluate the degree of cut breakage of lodging sugarcane, which is more conducive to the numerical quantification of key parameters. It is concluded that the inverted angle of lodged sugarcane lifting greater than 45° can make the cutting breakage degree of perennial root less than 1.6, which can not only provide reference for the existing sugarcane harvester operation but also provide key guidance for the optimization design of the SLS. The rest of the paper is organized as follows: Section 2 presents a brief analysis of the kinematic characteristics of the SLS. The simulation and analysis of the SLS is in Section 3. In Section 4, the materials and methods of the experiment are introduced. Section 5 focuses on the results and discussion of the experiment. Conclusions are drawn in Section 6.

2. Analysis of the Working Principle and Parameters of the SLS

2.1. Working Principle of the SLS

The SLS consists of a sugarcane lifter (also known as a crop divider), a double-disc cutter, a sugarcane press roller, a frame, etc. It is also called the “cutting table” of the harvester, and its structure is shown in Figure 2. The SLS’s primary function during the sugarcane harvester’s field operation is to lift the fallen sugarcane, cut its stalk near the roots, and transfer it to the conveying lane. The role of the sugarcane press roller is to press the upright sugarcane to a certain angle to facilitate the cutter’s smooth cutting of its roots.

2.2. Analysis of Operational Parameters of SLS

The function of the SLS is to complete the lifting and cutting of sugarcane stalks. Lifting the fallen sugarcane smoothly is the difficult part of the lifter’s operation. The inverted sugarcane stalks are in contact with the spiral blades, which on the one hand, move along the axial direction of the sugarcane roller, and on the other hand, produce a specific rotation with the roots of the stalks as the fulcrum. The kinematic model is established by choosing any moment of contact between the sugarcane stalk and the spiral blade, as shown in Figure 3, with the contact point O₁ and the roller radius r. The lodged sugarcane is mainly subjected to the friction force between the spiral blades, and the direction of the force of the spiral blades on the sugarcane stalk should form a friction angle ρ with its normal angle, ignoring the influence of the forward velocity of the harvester on the cane support process and setting the rotational speed of the drum as ω.

The sugarcane stalk generates a linear velocity v₀ under the rotation of the lifting drum in the direction tangential to the rotation of the contact point.

$$v_0=\omega r$$

(1)

The contact point O₁ of the sugarcane stalk and the spiral blade produces a sliding velocity v_n relative to the spiral surface and parallel to the tangential direction of the spiral line at the contact point. Since the sugarcane stalk and the spiral blade have a frictional effect, the direction of the combined velocity of the sugarcane at the contact point should be within the normal deflection friction angle ρ, which can be obtained as the combined velocity v. The velocity v is compounded by the axial movement along the drum and the radial circumferential motion, forcing the sugarcane to lift upward and gather between the rows, generating the circumferential speed in the radial direction as v_t and the axial speed as v_s, as shown in Figure 3.

$$v_{\mathrm{s}}=v\cos (\alpha +\rho )$$

(2)

$$v_{\mathrm{t}}=v\sin (\alpha +\rho )$$

(3)

The absolute velocity of motion v_n and the combined velocity v are obtained from the analysis of the motion of the contact point as:

$$v_{\mathrm{n}}=v_0\sin \alpha$$

(4)

$$v=\frac{v_n}{\cos \rho }$$

(5)

The axial velocity is obtained from the angular relationship v_s as:

$$v_s=v_0\frac{\sin \alpha }{\cos \beta }\cos (\alpha +\rho )$$

(6)

According to the motion model, the velocity v_t is the movement speed obstructing the sugarcane, and v₀ is the speed of the sugarcane driven by the roller:

$$v_0=\omega r=\frac{n\pi }{30}\frac{P}{2\pi \tan \alpha }=\frac{Pn}{60\tan \alpha }$$

(7)

$$v_s=\frac{Pn}{60}{\cos }^2\alpha (1-\tan \rho \tan \alpha )$$

(8)

Combining the above equations yields:

$$v_s=\frac{Pn}{60}\frac{1-f\frac{P}{2\pi r}}{{(\frac{P}{2\pi r})}^2+1}$$

(9)

where P is the pitch of the spiral blade, with the unit of mm; n is the rotational speed of the lifting drum, with the unit of rpm; f is the coefficient of friction; and α is the spiral lift angle of the spiral blade, with the unit of °.

According to the analysis of the motion of the SLS, it is known that the lifting of the fallen sugarcane before the cutting of the cane stalk can effectively improve the quality of the cut; it satisfies the results of previous studies [18,29].

$$\frac{l}{v_s}\le \frac{x}{v_m}$$

(10)

where, l is the total length of the sugarcane roller, with the unit of m; x is the horizontal distance between the foremost end of the sugarcane roller and the cutter tip, with the unit of m; and v_m is the forward speed of the machine, with the unit of m/s.

The analysis of Equations (9) and (10) and Figure 3 shows that many factors affect the lifting efficiency of inverted sugarcane, which mainly include diameter and pitch, etc., which can be subsequently carried out for parameter optimization. However, under specific parameters, using a sugarcane lifter to lift fallen sugarcane is the key to reducing sugarcane cutting breakage. This has been confirmed in relevant studies [9,30]. Based on Equation (10), it can be assumed that the lifting height of fallen sugarcane is closely related to the forward velocity of the harvester and the cutting breakage of the perennial roots, but no in-depth studies have been conducted in related literature to investigate the relationship between the lifting height of the fallen cane and the cutting breakage of the perennial roots. Therefore, it is essential to explore the relationship between the lifting height of the stalk and the cutting breakage.

3. Simulation Analysis of SLS

In order to facilitate the analysis of the SLS co-working, the ADAMS 2019 software established a rigid–flexible coupling simulation model of the SLS. Rigid–flexible coupling simulation technology has a wide range of applications in the field of agriculture, and the establishment of flexible sugarcane can more realistically restore the movement characteristics of the interaction between the sugarcane harvester hoist and the stalk during the actual operation [30]. The sugarcane stalk was set as a homogeneous flexible body with a length of 3 m. The simulation parameters were selected through the existing research [30,31,32,33]. The vertical height of the center (VHC) was chosen as the measure of the lifting height, as shown in Figure 4, which is calculated in Equation (11). In order to investigate the variation pattern of the lifting height from its root to the end point of the cutter blade, the sugarcane press roller was adjusted to the highest position in the test. The inverted posture of sugarcane was selected as a side fall, the fall angle was 15°, and the forward velocity of the SLS was set to 2 km/h. The movement process of sugarcane stalks under the SLS operation is shown in Figure 5.

$$h=\frac{H}{2}\sin \delta$$

(11)

where, h is the VHC of the sugarcane stalk, with the unit of mm; H is the effective total length of the sugarcane stalk, with the unit of mm; and δ is the inversion angle of the sugarcane stalk, with the unit of °.

According to Figure 5, with the advance of the random tool and the rotation of the lifting drum, the lodging sugarcane is gradually raised under the action of the sugarcane lifter, the cutter moves forward with the machine, and the horizontal distance between the root of the sugarcane stalk and the cutter blade is gradually shortened. Finally, the blade operation range of the cutter is reached. As shown in Figure 6, the change of the VHC and the distance between its root and the blade tip of the cutter during the lifting of the three sugarcanes’ rightmost stems are selected. The red curve is the change curve of the VHC, and the blue is the horizontal distance between the stem root and the blade tip. It is a linear relationship with the advance of the machine. According to the change of stem position during the SLS operation, the coordinated operation of the sugarcane lifter and cutter is critical in ensuring the quality of the stem cutting. If the cutter’s blade is too close to the stem root, there will be lodging in the forward horizontal direction. Before the sugarcane is lifted, the cutter starts cutting the stem root. If the distance is too far, the stalk may be lifted to a certain height, but it will stay at the upper end of the sugarcane supporting roller for a long time, which may hinder the lifting effect of the sugarcane supporting device on other lodging sugarcane, especially when the lodging amount of sugarcane is large; it can easily lead to the blockage of the feeding inlet.

In summary, to improve the operational efficiency and quality of the cane-holding–cutting system, it is necessary to conduct an experimental study between the lifting height and cutting quality of different inverted canes within the normal operating parameters of the machine. This can clarify the mutual influence mechanism between the lifting height of the stalk and the quality of lodging cutting. It can guide the optimization of reasonable spatial layout and the SLS’s priority operating parameters.

4. Materials and Methods

4.1. Test Platform

In this paper, the 4GQW medium-sized sugarcane harvester was used as the object of study. The two key components, the sugarcane lifter and cutter, were selected with the same parameters as the harvester. The overall structural model of the simplified test stand is shown in Figure 7. Figure 7a shows the SLS test stand. Figure 7b shows the hydraulic drive station, driven by a 45 kw diesel engine, whose primary function is to move the hydraulic motor to the cutting blade at high speed. For the experiment, the fixation of sugarcane stalk roots was referred to in the study of Chen [34].

4.2. Test Factors and Levels

According to the different degrees of sugarcane collapse and collapse angle, different VHCs were selected as the test factors. The VHC was selected as a reference for sugarcane in severe and moderate collapse (10° ≤ δ ≤ 60°) conditions, and the range of height at this time was calculated as (0.26 ≤ h ≤ 1.29 m). It is known from theoretical calculation and field tests that when VHC is 1.29 m, the maximum lifting height of the sugarcane lifter is reached; the highest position of the lifter roller was modulated during the test. In addition, the forward velocity (1~3 km/h) and the cutter rotational speed (550~650 rpm) were selected as the test factors. The established orthogonal test level coding table is shown in

Table 1. Test factor level coding table.

Code Value	Test Factors
	VHC m (X1)	Forward Velocity km/h (X2)	Cutter Rotational Speed rpm (X3)
1.681	1.3	3.0	650
1	1.1	2.6	630
0	0.8	2.0	600
−1	0.5	1.4	570
−1.681	0.3	1.0	550

. For the simulation, the horizontal distance between the foremost section of the lifter and the cutter blade was set to be about 2.11 m. A rectangular blade with an edge angle of 16.5° was selected for the test, and the material was 65 manganese steel. The effective cutting length of the blade was 80 mm, the width was 90 mm, the thickness was 6 mm, and the number of blades installed in a single disc was 4, evenly distributed. The diameter of the blade was 485 mm, and the inclination angle of the blade was set at 12°.

4.3. Evaluation Indicators

The quality of the cut ratoon mainly measured the performance of the cutter of the sugarcane harvester. The statistical indicators mainly included the broken head rate and the damaged form of sugarcane stalk. The broken forms of the cut ratoon mainly included whether it was damaged, such as slight sugarcane skin damage, severe sugarcane skin damage, slight sugarcane splitting, splitting damage, severe splitting, or bursting [35]. In order to facilitate the mathematical optimization of the indexes, this paper numerically quantified the effect of the breakage on host germination in combination with the form of breakage [36], which was graded and summed to 10, as shown in

Table 2. Forms and grades of ratoon cutting damage.

Broken Forms	Damage Effect Drawing			CBG
No damage				0
Slight sugarcane skin damage				1
Severesugarcane skin damage or slight sugarcane splitting				2
Splitting damage				3
Severe splitting and bursting				4

. Referring to the evaluation standard of JB/T6275-2007 [37], the crack over the node of the cut of the lodging root could be recognized as lodging head breakage, so reducing the cutting breakage grade (CBG) of the sugarcane stalk was a direct way to reduce the head breakage rate. The average diameter of the test sugarcane roots was 30.55 mm, and the average height of the stalks was 2859 mm. Each group of tests was repeated five times, and the degree of broken hosts after each test was graded correspondingly, as shown in Table 2. Finally, the average value was taken as the result of the evaluation index of that group of tests.

5. Results and Discussion

5.1. Test Results

A three-factor, five-level analysis test was designed using the Box–Behnken central combination of Design-Expert 12 software, and a total of 20 sets of tests were conducted. The test combinations and results are shown in

Table 3. Bench test results.

Test Serial Number	Test Factors			Evaluation Indicators
	X1	X2	X3	Y
1	0	0	0	1.2
2	−1.681	0	0	3.2
3	1	−1	−1	0.8
4	0	0	1.681	2
5	0	0	−1.681	1.8
6	−1	−1	−1	2
7	1	1	1	1.2
8	0	−1.681	0	0.8
9	0	1.681	0	2.6
10	1.681	0	0	1.4
11	1	1	−1	1.2
12	0	0	0	1.8
13	0	0	0	1.2
14	0	0	0	0.8
15	0	0	0	1.6
16	−1	−1	1	1.6
17	−1	1	−1	2.4
18	−1	1	1	2.2
19	0	0	0	1
20	1	−1	1	0.8

, where X₁, X₂, and X₃ are the factor level values, and Y indicates the CBG.

5.2. Significance Analysis of CBG

The results of ANOVA for CBG were obtained by analyzing the data shown in

Table 4. Analysis of variance of the test factor on the CBG of ratoon.

Source of Variance	SS	df	MS	F	p
Model	6.73	9	0.7473	4.09	0.0192 *
X1	3.82	1	3.82	20.95	0.0010 **
X2	1.71	1	1.71	9.34	0.0121 *
X3	0.0051	1	0.0051	0.0279	0.8707
X1X2	0.0050	1	0.0050	0.0274	0.8719
X1X3	0.0450	1	0.0450	0.2465	0.6303
X2X3	0.0050	1	0.0050	0.0274	0.8719
X12	0.9981	1	0.9981	5.47	0.0415 *
X22	0.0375	1	0.0375	0.2056	0.6599
X32	0.2136	1	0.2136	1.17	0.3048
Residual	1.83	10	0.1826	–	–
Loss of proposed items	1.13	5	0.2265	1.63	0.3017
Pure error	0.6933	5	0.1387	–	–
Total value	8.55	19	–	–	–

Note: SS is the sum of squares; df is freedom; MS is mean squares; * shows this term is significant (0.01 < p < 0.05); ** shows this term is highly significant (p < 0.01). X₁, X₂, and X₃ are the code values of the test factor.

. The regression model was obtained as significant (p < 0.05), and the misfit term was not effective (p > 0.05), indicating that the regression model and the data fit well. The VHC was highly significant, the forward velocity was substantial, and the order of influence of each factor on the CBG of the VHC was the VHC > the forward velocity > the cutter rotational speed. The regression equation of the test factors on the CBG of the lodging cut was obtained as:

$$Y=1.28-0.529X_1+0.356X_2+0.263X_1^2$$

(12)

5.3. Response Surface Analysis

The response surfaces of the interaction factors in the VHC, the forward velocity, and the cutter rotational speed to the CBG obtained by Design-Expert 12 software are shown in Figure 8. When the rotational speed of the cutter is 600 rpm, the effect of the interaction of the VHC and the forward velocity on the CBG is shown in Figure 8a. The CBG increases with the increase in forward velocity, but changes slowly. The VHC and the CBG are negatively correlated; with the lifting height decreasing, the CBG gradually increases. When the sugarcane is severely fallen, its CBG is more significant than 2.0 levels at a different forward velocity, and the CBG increases with the increase of the forward velocity. When the forward velocity is 3 km/h, the average CBG reaches about 3.7; as the VHC increases, the CBG gradually decreases. The effects of the interactions of the VHC and cutter speed on the CBG at the forward velocity of 2 km/h in Figure 8b increase as the VHC decreases. Figure 8c shows the interaction effect of the forward velocity and cutter speed on the CBG when the cane lifting height is 0.8 m. At this time, the variation of the CBG is slight, and the CBG is about 2.2 under this condition.

5.4. Experimental Results and Discussion

According to the numerical analysis of the response surface in Figure 8a, it can be predicted that when the VHC is between 0.3~0.55 m and the forward velocity is between 1~3 km/h, the average CBG of sugarcane lodging is between 1.5~3.7. When the VHC is between 0.55~0.8 m and the forward velocity is about 2.5~3 km/h, the CBG of lodging cutting is about 1.7~2.8; when the forward velocity is between 2~2.5 km/h, the CBG is about 1.3~2.3; and when the forward velocity is between 1~2 km/h, the CBG is about 0.9~1.8. When the VHC is 0.8~1.3 m and the forward velocity is 2.5~3 km/h, the CBG is about 1.4~2.0; when the forward velocity is 1~2.5 km/h, the CBG is less than 1.6. The CBG is about less than 1.0 when the forward velocity is 1~2 km/h.

Figure 8b shows the results of the response surface of the VHC and the cutter rotational speed to the CBG, which can be predicted: when VHC is 0.3~0.5 m, the CBG is about 2~3.5; when the VHC is in 0.8~1.3 m, CBG is between about 1.0~1.3.

Figure 8c shows the response surface of forward velocity and the cutter rotational speed to the CBG, which can be predicted: when the forward velocity is between 2~3 km/h, the CBG is about 1.3~2.3; when the forward velocity is between 1~2 km/h, the CBG is about 0.9~1.5.

Since the selected range of the cutter rotational speed was not significant during the test, its effect on the CBG was not considered. In this paper, each combination of tests was repeated five times, and the CBG should be a whole number, considering the effect of the breakage grade of 2.0 on the growth of hosts. Considering the efficiency of the harvester operation, stalk breakage, and germination, this paper chose the average CBG ≤ 1.6 as the qualified classification standard for the lodging cut breakage. A comprehensive analysis of the results in Figure 8 showed that when the forward velocity was 1~3 km/h, the standard of perennial root-cutting breakage was satisfied when the lodged sugarcane was lifted by the VHC about 0.85~1.0 m. According to Equation (11), it was calculated that the inverted angle of sugarcane was about 35~42° at this time. This value was obtained under an ideal field, and considering the complex environment in the field, the inverted angle of the stalk was selected as 45° to measure the standard of whether the lifting height of the spiral sugarcane lifter for the inverted stalk was qualified.

The compilation of related literatures found that previous studies were conducted separately for both the sugarcane lifter and the double-disc cutter. For example, Hu et al. [11] explored the effects of parameters such as forward velocity and sugarcane lodged angle on the operational performance of the sugarcane lifter through field test methods and pointed out that the intertwining of lodged sugarcane would cause the stems to be uprooted during the cutting process. It was necessary to further improve the operational performance of the sugarcane lifter. The presence of severely fallen cane was a critical reason for the high rate of lodging cut breakage, as shown repeatedly by Wang and Liu et al. [13,22] in their studies conducting cutters. Related studies have shown that the lifting height of the sugarcane lifter for fallen sugarcane had a more important effect on the CBG of lodging, but the role relationship between the effect of the lifting height of sugarcane on the lodging cut breakage has not been further investigated. In this study, the lack of this previous study was compensated exactly. It was found through the experiment that the lifting height of the fallen stalk is the key to the quality of the lodging cut breakage, and this finding and the results obtained from the experiment can provide a key guiding role for the optimal design of the cane-holding–cutting system of a sugarcane harvester, especially a medium-sized sugarcane harvester.

6. Conclusions

In this paper, a medium-sized sugarcane harvester was used as the research object to classify the degree of cut breakage of the lodging roots into grades by using the numerical quantification method. The effect of the VHC on the CBG of lodging was highly significant, and the stalk CBG decreased with the increase in lifting height. It was concluded that the lodged angle of the stalk lift by the elevator that is greater than 45° can make the stalk CBG less than 1.6. The inversion angle of 45°, at which the stems are lifted, can be used as an evaluation criterion to measure the quality of the lifter’s work. Future works should carry out the multi-parameter collaborative optimization design of the SLS to explore low-loss and high-efficiency sugarcane harvester operating parameters.