Bionic Design of a Winding Roller and Experiments for Cleaning Long Foreign Matter from Raw Cotton

Abstract

Natural cotton fibers are inevitably mixed with long foreign matter (LFM) from the planting and ginning processes, which greatly deteriorate the quality of textile products. Therefore, how to design automated equipment that can efficiently remove LFM is very important for the cotton industry supply chain. Inspired by the comb-like gill rake structure of the carp (cyprinus carpio), a structural bionic method is first proposed for the development of automatic equipment. A series of key parameters of the proposed bionic design are presented and further optimized based on the orthogonal experimental design algorithm and the designed experimental automatic equipment through a sensitivity analysis between the factors (key parameters) and response (LFM removal efficiency). The design results show that the tooth length of the winding roller is the most significant factor effecting the response. Experimental results demonstrate that the designed modular comb-like winding device has great potential for application in the industrial cotton supply chain. Moreover, the structural bionic method is an applicable and promising method to develop this equipment compared with traditional design ideas.

1. Introduction

As a natural fiber, cotton has been used in a wide variety of fields, such as textiles, pharmaceuticals, chemistry, printing, and other national industries. As one of the most important cotton-growing countries, nearly 30% of the cotton fibers in the world are produced in China [1,2]. As we all know, cotton fiber is unique in its strong, durable, safe, healthy, and breathable characteristics, which may be not be replaced by other unnatural synthetic fabrics. However, contamination matter is inevitably mixed into the cotton fibers during the whole process of cotton production. This may dramatically affect the performance of textile products.

Many existing investigations have indicated that the contaminated contents of machine-harvested cotton in Xinjiang province, China, account for 8% to 27% of the total content [3]. In practice, long foreign matters (LFM) such as long hair, binding ropes, plastic films, chemical fibers, polypropylene, and twines inevitably become mixed into the cotton during the planting, picking, and treatment processes. This greatly deteriorates the quality of the textile and decreases the monetary value of cotton products. Moreover, the price of hand-cleaned cotton is higher (about $USD 120/ton) than UN-cleaned under standard commercial conditions. In this case, cotton processing enterprises have to hire many people to clean the contaminants, which in turn intensifies the economic burden [4,5]. Furthermore, all Chinese cotton enterprises are facing critical challenges in the international cotton market.

Generally, microtrash or coarse trash such as sticks, leaves, dust, and metal particles can be removed by a centrifugal fan or other operations. However, the LFM in raw cotton is mostly longer than 4 cm, and a small amount of LFM may be crushed or torn during ginning, which makes it more numerous and more difficult to clean. Therefore, the LFM in raw cotton must be completely removed before ginning [6]. Over the past decades, the manufacturing system of the cotton industry has changed a great deal; smart agriculture is booming, and smart manufacturing technology is the mainstream today [7]. Recently, different varieties of automatic detection technologies have been proposed based on differences of LFM from cotton in color, shape, or other properties. Moreover, the machine vision method is the most important technology in realizing the identification of LFM [8,9]. Many methods, such as CT X-rays [10,11], ultraviolet [12], multi-band image fusion, and more have been proposed [13]. However, the majority of the above methods mainly focus on the lint cotton stage, which can be identified as the second processing procedure in the ginning of raw cotton. In this case, even the highest contamination removal efficiency may be limited to only 85% owing to a larger shattered LFM quantity in many systems [14]. At present, Chinese enterprises usually adopt a manual picking process for the pre-cleaning of raw cotton LFM. However, this process has several disadvantages. The efficiency of manually picking long fibers is about 1 ton/day, the cost is CNY 200–300 per person, and the cost of manual picking for enterprises is about 2–3 million CNY/year; moreover, due to such factors as visual fatigue and physical fatigue of workers, it is difficult to ensure the efficiency and precision of workers in picking LFM.

Unfortunately, although there are many disadvantages in the manual picking process, it remains a widely used sorting method. LFM-scavenging technology in raw cotton needs to be developed. Designing automatic LFM scavenging equipment has become one of the top priorities in China’s cotton industry [15]. To date, little automatic mechanical equipment has been developed to remove LFMs mixed in raw cotton. The reasons for this can be summarized as follows:

(1)

The environment of raw cotton processing is seriously polluted, which is difficult for optical devices;

(2)

Raw cotton is compressible in bundles and has non-uniform thickness, which results in low control precision;

(3)

Cotton planting, picking, and cleaning are dispersed in rural areas, where automation is difficult.

Therefore, although the results are unstable and unreliable, manual picking has been a feasible method over the past few decades. On the other hand, with the maturity and development of intelligent agricultural technology, mechanization is being popularized in the relevant fields of agriculture, and agricultural automation equipment is expected to gradually replace manual work. In order to free hands, improve the efficiency and rejection rate, and reduce production costs, it has become an urgent need to develop automatic cleaning technology and automatic cleaning equipment for raw cotton LFM. As a key factor in LFM cleaning, an optimized LFM winding roller can maximize removal efficiency and minimize fiber damage to the cotton. This paper takes the gills of the carp fish as its research object. Through in-depth study of its gill structure and working principle, it is known that the comb-shaped gill rake of the carp can effectively filter phytoplankton and food particles from water through the gap between the gill arches. The gill rake of the carp is usually arranged in one or two rows of each gill arch, and their number, spacing, and form are usually different. Consequently, inspired by the comb-like gill rakes in carp (cyprinus carpio), a novel winding roller with a structural bionic method is first proposed, and automatic mechanical equipment is developed. Compared with the current removal technology, the carp-shaped winding roller based on carp gill rakes proposed in this paper can adapt to complex environments and has a removal effect which can meet the requirements of the cotton industry.

The remainder of this article is organized as follows. The second part introduces the design of the winding roll, the feeding roll, and the overall system based on the bionic structure. The third section introduces the principle of orthogonal experiment design, specific flow, and analysis. The fourth part illustrates the experimental results and discusses them. Finally, our conclusions are drawn in Section 5.

2. Materials and Methods

2.1. Sample Morphology of Gill Rakes in Carp (Cyprinus Carpio)

In practice, using analogous structures in nature in conventional design problems can help designers to find efficient solutions [16,17]. There are many examples in which imitating the morphological mechanisms of natural organisms and applying them to human production and life has made full use of the characteristics of natural organisms to achieve good results in application. The comb-like structure of carp gills effectively filters phytoplankton and food particles from the water while removing impurities. Inspired by this, in this paper the comb structure of the carp gill was studied in detail, then this bionic structure was applied in the field of agriculture to design automatic mechanical equipment. Below, the composition and working principle of carp gills are introduced in detail.

The carp (cyprinus carpio) is studied in this paper due to its gill structure. The gills are the main sites of gas exchange in fishes and play the most important role in feeding. As shown in Figure 1, the gill is mainly composed by gill rakes, gill arches, and gill filaments [18,19]. In addition, the gill arches are equipped with gill rakes toward the anteromedial side opposite to the gill filaments. The prick-shaped gill rakes are bony or cartilaginous, their length is 2–3 mm, and they are arranged in equal spacing. This is considered to play an indispensable role in retention and transport of food for swallowing. In addition, similar to the mechanism of a whale’s baleen, the comb-like gill rakes can efficiently filter plankton and food particles from the water through the existing spaces between the gill arches. The gill rakes of a carp are usually arranged in one or two rows each, and their number, spacing, and form are varied. This can be recognized as an evolution of the food-trapping mechanism.

2.2. Bionic Design of a Winding Roller

Structural bionics is an innovative design method distinct from traditional design methods. In terms of cottons, most LFM is mixed with raw cotton after picking, and the length is usually greater than 3 cm. As stated above, the LFM must be removed prior to ginning process, otherwise it is broken into pieces, degrading the lint. To a certain extent, fish are characterized by densely spaced, elongated, comb-like gill rakes, which simultaneously eliminate plankton or other particles when water passes through the teeth. From the point view of structural bionics, the cotton layer is similar to the stream of water during the feeding process. Therefore, the clearing principle of LFM is similar to the principle by which the gills clear plankton or other particles. In this case, LFM can be easily winded and separated before separating the cotton seed from the lint due to their length and different properties from lint. Therefore, LFM can be easily cleaned by a similar structure to the comb-like gill rakes. Moreover, the design of the bionic structure minimizes the fiber damage to the lint and seed as it passes through the comb-like process.

In terms of the design of the bionics structure, elaborating the design of the geometry and dimensions of the winding roller is the key technology for high LFM cleaning efficiency. Here, two factors should be considered. First, in the design of a single winding roller mimicking the comb-like gill rakes, the shaft of the winding roller is used to imitate the gill arch of a carp and the teeth on the winding roller are used to imitate the comb structure of the gill rake. Because the gill rake of a carp is usually arranged in one to two rows on each gill arch, the teeth on the shaft of the winding roller are designed in multiple rows, four rows in this design. The second factor is the design of the multi-roller configuration based on the single winding roller; different multi-roller configurations may lead to differences in cleaning efficiency. As shown in Figure 2, the roller is designed considering manufacturing convenience and feasibility, which includes equally-spaced winding teeth welded onto a shaft and placed vertically in four rows along the axial line. The interlaced arrangement of the teeth can interact with other rollers, and can increase cleaning efficiency in the designed multi-roller configuration.

Each roller is a simply supported beam with two bearings, and is driven by a chain. According to the productivity of a plant, the width of the cleaning device room is designed as 2000 mm. The key design parameters of the teeth are D (diameter), L (length), and S (spacing). The teeth must be designed and optimized to enhance the cleaning efficiency.

2.3. Module Design of Multi-Roller Cleaning Device

To improve the cleaning efficiency of the mechanical device, a multi-roller module was designed. As shown in Figure 3, a standard module includes two feeding rollers and four winding rollers. Each module’s side dimension is 600 × 600 mm. To meet different cleaning requirement, the multi-module configuration can be arranged in parallel based on the standard module. In this paper, equipment with three modules is proposed.

The multi-roller functioning of a standard module is listed as follows:

• First stage: cotton feeding. The two above feeding rollers have large dimensions and load-bearing ability. As shown in Figure 4, when the raw cotton is loaded from the upper inlet, the feeding rollers rotate in opposite directions at a low speed of 3–6 r/min. In this case, uniform cotton flow is formed under gravity and extrusion, and is transported downward simultaneously. The forces are mainly loaded on the feeding rollers, which need mechanical calculation.
• Second stage: LFM rough winding. The adjacent winding roller below each feeding roller has a high rotation speed. The cotton flow mixed with LFM is separated layer-by-layer via interaction with the teeth. Then, the cotton layer is transported by the centrifugal force, and the LFM on the teeth can be cleaned during rotating and winding.
• Third stage: precise LFM winding. The cotton layer interacts with the teeth of the lower winding rollers again to further clean the LFM, and the cleaning principle is similar to the second stage. When the cleaned cotton layer reaches the outlet, a vacuum tube collects it for the next process.

Based on practical experience, the rotating speed of the feeding roller was designed as 3–6 r/min based on the requirements of a stable cotton supply and hard structural stiffness. Here, the key parameter of the equipment is the diameter design of the feeding roller, designed as follows.

The weight of the cotton placed on every module is nearly one ton. Because the feeding rollers rotate in opposite directions and the cotton is highly compressed, another one ton of extrusion force is generated. In this paper, the above forces is derived from test data from the Shandong FuHao Optoelectronic Technology Co., Ltd. (Jinan, China). The maximum deflection of the feeding roller is calculated by

$${\omega }_{\max }=\frac{5q{L}^4}{384EI}=\frac{5\frac{G+F_{extru}}{L}{L}^4}{384E\frac{\pi D_{{}^f}^4}{32}}=\frac{5(G+F_{extru})L^3}{12E\pi D_f^4}\le 10 \mathrm{m}\mathrm{m}$$

(1)

where $G$ is the weight of cotton, $F_{extru}$ is the extrusion force, E is the elasticity modulus of steel, I is the inertia moment of the cross section, L is the length of the feeding roller, $D_f$ is the diameter of the feeding roller, and ${\omega }_{\max }$ is the maximum deflection, which is limited to 10 mm as test data for vibration control. If it is over 10 mm, the roller’s deflection is obvious and the transmission system overloads. The vibration of the chain is dangerous and unavoidable.

In addition, the diameter can be calculated by a modified equation (Equation (2)), based on Equation (1), as follows:

$$D\ge \sqrt[4]{\frac{5(G+F_{extru})L^3}{12E\pi {\omega }_{\max }}}=\sqrt[4]{\frac{5\cdot ({10}^4+{10}^4)\cdot {2000}^3}{12\cdot 210\cdot {10}^9\pi \cdot 10}}=56 \mathrm{mm}$$

(2)

Therefore, the diameter of the feeding roller is designed as 60 mm. The length and diameter of the feeding teeth are 120 mm and 18 mm (as shown in Figure 3), respectively, which can be calculated from the above procedures considering the equipment dimensions.

To separate cotton and wind LFM, the speed of the winding roller is designed with a high value. According to test data, the forces are non-significant design factors and the speed is the most significant factor. As shown in Figure 3, the horizontal space in the winding rollers is about 200 mm, the diameter of the roller shaft is 30 mm, and the tooth length is limited to 70 mm.

2.4. System Setup

In this paper, LFM cleaning equipment is designed; the corresponding three-dimensional model is shown in Figure 5. The main parameters of the system are listed in

Table 1. Main parameters of LFM cleaning system.

Dimensions	Maximal Feeding Capacity	Power of Centrifugal Blowers	Power of Electric Motors
2000 × 1800 × 4000 mm	5 ton/h	10 kW	5.5 kW

. In particular, two kinds of drive motors are deployed for different speeds of the feeding and winding rollers.

3. Experiments

3.1. Investigated Model

An equipment with three cleaning modules was developed. The corresponding experiments were tested in a cotton processing plant. Two models of feeding teeth are proposed to test the LFM winding efficiency; the advantages and disadvantages are as follows.

First, the design of the thread teeth is presented. Although these teeth provide high cleaning efficiency, the presence of threads causes the cotton fiber and LFM to intertwine simultaneously. When cotton fiber becomes stuck in the teeth, the cleaning quality declines and maintenance becomes time-consuming. Second, a design using rounded tooth is put forward. These can effectively wind LFM, and are is simple to manufacture and convenient to maintain. Although the cleaning quality is only middling, this design meet the requirements.

After comparing the advantages and disadvantages of threaded teeth and filleted teeth, we chose filleted teeth after comprehensive consideration.

3.2. Orthogonal Experimental Design (OED)

The OED method is regarded as a modern method and plays an irreplaceable role in experimental design. It has successfully saved a large amount of money and time in acquiring the optimum level group [20]. The key technology of the method is an experimental arrangement with an orthogonal array based on the reasonable and representative levels of the investigated factors [21,22]. The orthogonal array is a design sequence according to a set of rules. The orthogonal array is represented as La(bc), where L is the orthogonal array, a is the number of experiments, b is the level of factors, and c is the number of factors or the number of columns.

3.3. Analysis Based on OED

In this study, the factors that affect the cleaning efficiency of the winding rollers are investigated based on the OED method. The experimental process of the OED method is shown in the Figure 6. As shown in

Table 2. Levels and factors affecting LFM cleaning quality.

Factors		Level
Parameters	Abbreviation	1	2	3
Tooth Diameter	D (mm)	5	6	8
Tooth Length	L (mm)	50	60	70
Teeth spacing	S (mm)	60	70	80
Shaft speed	V (r/min)	300	400	500

, four factors, including the diameter (Factor A), length (Factor B), and spacing (Factor C) of the teeth and the rotating speed of the roller shaft (Factor D) are investigated, and three levels of each factor are defined. Here, $L_9^{}(3^4)$ is employed to assign the considered factors, as shown in

Table 3. Scheme and results of orthogonal experiments.

No.	D	L	S	V	Collected LFMs Amount (g/ton)
1	5	50	60	300	12.2
2	5	60	70	400	13.3
3	5	70	80	500	15
4	6	50	70	500	15.6
5	6	60	80	300	13.2
6	6	70	60	400	16.7
7	8	50	80	400	15.1
8	8	60	60	500	13.4
9	8	70	70	300	15.6

, which is an orthogonal sequence of the four factors with three levels each. Nine trials were carried out to achieve the optimization process according to $L_9^{}(3^4)$. More importantly, the OED method can reduce the required number of experiments from 81 to 9. Every experiment with different levels of the factors has been tested in practice, and the corresponding amount of LFM was measured and listed after processing.

4. Results and Discussion

As shown in Figure 7, the developed LFM cleaning equipment is able to gather and clean all of the LFM at intervals. The cotton can be fed from the top rollers and cleaned by the winding rollers. Moreover, jamming among teeth can be avoided owing to the comb-like structure.

For every experiment, 20 g of LFM, including long hair, plastic films, chemical fibers, and polypropylene twine were mixed uniformly into one ton of raw cotton, and every experiment was repeated three times to obtain authentic results. Because the speed of the feeding roller is determined by the moisture content of the cotton, it has large influence on the extrusion force and feeding efficiency. As shown in Table 3 and

Table 4. Range analysis data.

Value Name	D	L	S	V
${\overline{K}}_1^{}$	13.50	14.30	14.10	13.67
${\overline{K}}_2^{}$	15.17	13.30	14.83	15.03
${\overline{K}}_3^{}$	14.70	15.77	14.43	14.67
$R_j^{}$	1.67	2.47	0.73	1.37

, nine experiments were carried out based on the $L_9^{}(3^4)$ matrix with uniform moisture content value (10%) and speed of feeding roller (5 r/min).

In a range analysis, there are two parameters, denoted by $K_{ji}^{}$ and $R_j^{}$. Here, $K_{ji}^{}$ is defined as the sum of the indexes of all levels at each factor $j$, ${\overline{K}}_{ji}^{}$ is the average value of each experimental factor at the same level $i$, $R_j^{}$ is defined as the range between the maximum and minimum value of $K_{ji}^{}$, and $K_{ji}^{}$ is used to evaluate the importance of the factors. If $R_j^{}$ is larger, this indicates greater importance of the factor. For example, for the $L_9^{}(3^4)$ matrix, the calculation for factor D is as shown below:

$$K_{D1}^{}=Y_1+Y_2+Y_3$$

(3)

$$K_{D2}^{}=Y_4+Y_5+Y_6$$

(4)

$$K_{D3}^{}=Y_7+Y_8+Y_9$$

(5)

$${\overline{K}}_{D1}^{}=\frac{K_{D1}}{3}$$

(6)

$${\overline{K}}_{D2}^{}=\frac{K_{D2}}{3}$$

(7)

$${\overline{K}}_{D3}^{}=\frac{K_{D3}}{3}$$

(8)

$$R_j^{}=\max ({\overline{K}}_{Di}^{})-\min ({\overline{K}}_{Di}^{})$$

(9)

where $K_{Di}$ is the value of level i of factor D and $Y_i$ is the value of the trial number i.

As shown in Table 3, the LFM amount varied from 12.2 to 16.7 g/ton.

The test shows the mean values of ${\overline{K}}_{ji}^{}$ for different factors with different levels, demonstrating that the higher the mean value of ${\overline{K}}_{ji}^{}$ is, the more significant the effect on LFM cleaning quality. Therefore, the best levels of the four factors corresponding to the highest value of $K_{ji}^{}$ are listed as follows: tooth diameter 6 mm, tooth length 70 mm, teeth spacing 70 mm, and rotating speed of the roller shaft 350 r/min.

In addition, the value of $R_j^{}$ demonstrates the significance of the four factors’ influence. More specifically, a larger $R_j^{}$ means a more significant effect on the LFM cleaning quality. From Table 4, it can be seen that the significance of factors can be sorted from high to low as follows: tooth length (2.47), tooth diameter (1.67), rotating speed (1.37), and teeth spacing (0.73).

Through calculation, it is easy to calculate the value of ${\overline{K}}_i$; because $R_j$ is defined as the range, the greater the value of $R_j$, the greater the impact of this factor on the LFM elimination effect. It can be seen from Table 4 that tooth length has the greatest effect, while tooth spacing has the least effect.

The bar chart in Figure 8 shows the influence of different factors. As can be seen from the figure, factor B (tooth length) has the greatest impact on the LFM elimination effect.

5. Conclusions

In this paper, a structural bionic method is proposed to design a winding roller for LFM cleaning equipment in raw cotton processing. Inspired by the structure of the gill rakes in carp, the equipment designed in this paper mimicked the comb-like structure of the gills. To evaluate LFM cleaning performance and efficiency, equipment with a three-module cleaning system was developed and experiments were carried out under the standard factory conditions. The tooth diameter, length, spacing, and rotational speed of the roller were taken as the testing factors and the effects of the comb-like rollers were examined using the OED method. Our results show that the optimal combination of the above testing factors is 6 mm, 70 mm, 70 mm, and 350 r/min, respectively.

More importantly, the method proposed in this paper based on the bionic structure has a good effect on the removal of LFM from raw cotton. It can deal with raw cotton from China and India well, effectively replace the current manual picking process, and solve the problems of the high cost, low efficiency, and difficulty of ensuring a steady removal rate that arise with manual picking. The winding roller designed here by simulating carp gill rakes can effectively remove LFM from raw cotton and is able to meet the requirements of the cotton industry. The biggest advantage of this winding roller design is that it can minimize damage to cotton fibers while effectively removing LFM.

At present, although the performance of the designed winding roller can replace labor, thereby reducing labor costs, its accuracy can be further improved. In the future, the method and equipment proposed here on the basis of a biomimetic structure needs to be further developed and improved. Photoelectric technology should be incorporated in order to carry out high-precision sorting to remove LFM in both the raw cotton stage and the lint stage.