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Design of Structural Parameters of Cutters for Tea Harvest Based on Biomimetic Methodology

Design of Structural Parameters of Cutters for Tea Harvest Based on Biomimetic Methodology Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 8798299, 8 pages https://doi.org/10.1155/2021/8798299 Research Article Design of Structural Parameters of Cutters for Tea Harvest Based on Biomimetic Methodology 1,2 2 2 1 1 Zhe Du , Yongguang Hu , Yongzong Lu, Jing Pang, and Xinping Li College of Agricultural Equipment Engineering, Henan University of Science and Technology, Luoyang 471023, China School of Agricultural Engineering, Institute of Agricultural Engineering, Jiangsu University, Zhenjiang 212013, China Correspondence should be addressed to Yongguang Hu; deerhu@163.com Received 21 April 2021; Revised 19 June 2021; Accepted 1 July 2021; Published 23 July 2021 Academic Editor: Donato Romano Copyright © 2021 Z He Du et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Owing to their sharp teeth, crickets can eat through new shoots of the stalks of tea plants. Inspired by the special geometrical structure of the teeth of crickets, this study designed a biomimetic cutter to reduce the force and energy required to cut the stalks of tea plants. Therefore, four biomimetic cutters were considered: a, b, c, and d. Cutter a was a traditional cutter used for comparison with the other three cutters, which were biomimetic. The cutters were manufactured using 3D printing technology and assessed by a texture tester at different loading speeds (5, 10, and 15 mm/s, respectively). The results show that cutter c delivered better performance compared to cutter a at loading speeds of 5, 10, and 15 mm/s, respectively. However, at 15 mm/s loading speed, the maximum cutting forces required for cutters b and c were 9.43% and 6.04% lower, respectively, than that for cutter a (9.021 N). Similarly, the energies consumed by cutters b and c were 13.8% and 4.24% lower than that consumed by cutter a (1.225 J). In addition, cutter c delivered the best results compared to others. Based on the study results, it was concluded that the biomimetic cutters can thus help to optimize the tea harvest. 1. Introduction energy [13]. Yamasaki et al. [14] and Galedar et al. [15] performed similar research on the structural parameters of the reciprocating cutter. Shi et al. [16] established the Tea is an aromatic beverage that is consumed all over the world [1]. Tea pluckers are widely used to improve the yield 3D models of crop stalks and cutters by using response of harvesting tea plants [2, 3]. The cutter is a key component surface methodology to determine the optimal combina- of the tea plucker that has a significant influence on its cut- tion of the kinematic parameters of the cutter at a cutting ting performance and efficiency [4, 5]. Commonly used cut- speed of 1.6 m/s, cutting angle of 15 , and working speed ters in tea pluckers include the reciprocating cutter, disk of 1 m/s. cutter, and flail-type cutter. Compared with the disk and Biomimetic technology has recently been applied to opti- flail-type cutters, the reciprocating cutter has a simpler struc- mize the design of traditional agricultural machinery and to ture and a wider range of adaptations [6–8]. Besides, it is improve its energy utilization [17–20]. It combines biological important to optimize the structural parameters of the recip- principles with engineering problems for developing solu- rocating cutter to improve its cutting performance. tions. A study by Chang et al. [21] designed a biomimetic Present research on the optimal design of the recipro- stubble cutter by imitating the outer contour of the foreclaws cating cutter has focused on its cutting speed, cutting of the nymph of the species Cryptotympana atrata for reduc- angle, geometry, and size. The mechanical properties of ing the cutting resistance. By considering the serrated inci- the plant have also been considered in the design of the sors of a grasshopper, Jia et al. [22] designed and cutter [9–12]. To design a harvesting element, a study by manufactured a biomimetic cutter to reduce the requirement Sunil et al. studied the mechanical properties of energy- of the maximum cutting force and cutting energy. Tong et al. cane stalks and found that the oblique angle and cutting [23] optimized a stubble-cutting disk based on the dynamics speed of the cutter had a significant effect on the cutting of the clawed toes of a mole rat as it digs the ground. Research 2 Applied Bionics and Biomechanics First sharp tooth Second sharp tooth Other teeth (a) (b) Figure 1: (a) Teeth on the mandible of the cricket. (b) Structure of the tea stalk. Table 1: Parameters of the curve. Parameters Curve a Curve b Curve c Curve d Curve e 3.248 –7.302 1283.896 41225.250 –16145.526 5.295 1.689 –32.294 –420.6120 107.581 0.104 –0.018 0.249 1.602 –0.263 a 7:08e − 05 –7:58e − 04 –2:70e − 03 2:83e − 04 –0.006 a 5:30e − 05 –1:04e − 07 8:00e − 07 1:69e − 06 –1:13e − 07 0.976 0.999 0.960 0.985 0.976 Curve a Curve b Curve c Curve d Curve e Figure 2: Extracted contour line of the teeth of the cricket. optimize the parameters of a cutter. For the aggression of the mouth structure to be adaptive, insects must decide what angle is best to eat. How it is done is arguably best understood in crickets (Orthoptera: Gryllidae) [29]. The cricket is an omnivorous insect that consumes the fresh shoots, stalks, leaves, and seeds of tea plants, vegetables, and other crops. The teeth in its mandible have evolved and adapted so that they can easily cut into and tear plant fibers [30]. Therefore, features of the teeth of the mandible of the cricket can be used to design an efficient cutter for tea plants. Based on the above discussion, the present paper exam- ines the structural parameters of cutters for harvesting tea plants based on biomimetic technology. The line of the outer 0 5 10 15 20 25 30 35 x (pixel) contour of the serrated structure on the mandible of the cricket is extracted, and its fitted curve was applied to design Figure 3: Best approximation of the fitted curve. a biomimetic cutter. In addition, four cutters (a, b, c, and d) were manufactured by using 3D printing technology, and experiments were carried out on a texture tester to investigate in bionics can be consulted to design a cutter that can their performance in terms of the required cutting force and reduce the energy and the cutting force needed for har- energy. Finally, the cross-section of the tea stalk was observed vesting [24, 25]. by using a microcomputed tomography (micro-CT) scanner Biomimetic cutting techniques are usually based on the to analyze the performance of the cutters. characteristics of phytophagous insects, such as the tiger bee- tle [26], bamboo weevil larva [27], and locust [28]. These 2. Materials and Methods insects have well-formed, strong mandibles to efficiently chew plants. Features of parts of their mouth can be used to 2.1. Cutter Design y (pixel) Applied Bionics and Biomechanics 3 14 16 18 20 22 24 26 28 30 32 34 0 2 46 8 10 12 14 16 18 x (pixel) x (pixel) Fitting data Fitting data Best approximation Best approximation (a) (b) Figure 4: Best approximation of the fitted straight line: (a) rising portion and (b) falling portion. express them at a given time. Finally, Origin software was Table 2: Parameters of the fitted straight line. used for data analysis to select the biomimetic units. Part b b R 0 1 2.1.4. Cutter Manufacture. The contours of the geometrical Rising portion 2.387 1.959 0.964 features of the teeth of the cricket were used in the design Falling portion 64.129 -1.891 0.953 of biomimetic cutters. To accurately express the biomimetic element, 3D printing was used to machine the cutter by using Future 8000 resin. It has a highly precise and smooth surface 2.1.1. Sample Preparation. For the present experiment, the and delivers a similar mechanical performance to that of adult crickets were collected from the suburbs of Ningyang acrylonitrile butadiene styrene (ABS). The 3D printed cutters city in Shandong Province, China. Five samples were narco- were used in all tests. Besides, the cutter material was still tized by 99% ether, and their teeth were taken out using twee- Future 8000 resin in the simulation test. zers and washed with distilled water. However, the tea samples were obtained from the Maichun Tea Farm in 2.2. Test Methods. The cutters used in the experiments were Danyang, Jiangsu, near the Yangtze River region (latitude 1.5~2.5 mm thick. Finite element analysis using ANSYS soft- ° ° ′ ′ 32 02 N, longitude 119 67 E). The experiment selected verity ware was carried out to determine the influence of the cutter tea, and the tea stalk was the third internode of the Zhongcha thickness on the cutting force. 108 variety. At the time of the sampling, the average moisture A texture tester (Stable Micro Systems, TA-XT2i) was content of the tea stalk was 73.8% (wet basis), and the picking used to measure, record, and analyze the cutting perfor- time was June 2019 [31]. mance (cutting force and time and energy consumed) of dif- ferent cutters on a tea stalk [32]. The tester had a wide range 2.1.2. Sample Observation. The geometric structure of the of moving distances of 0.1 mm–295 mm, and its accuracy of teeth of the crickets and the microstructure of the tea stalk force measurement was 0.025% at a speed of 0.1~20 mm/s. were observed by a digital microsystem (VHX-900F, KEY- The loading speed is an important factor because the tea stalk ENCE, Japan). This system was used to measure the 2D size was made of viscoelastic material [33]. In the cutting experi- and 3D outline of these objects. A photograph of the teeth on ments, the loading speeds were set to 5, 10, and 15 mm/s, the mandible of the cricket is shown in Figure 1(a), and the respectively. When the cutter was cutting the tea stalk at a structure of the tea stalk is shown in Figure 1(b). constant speed, the cutting force-displacement curve could be obtained with the texture tester. The energy consumed 2.1.3. Curve Extraction. TRACE software was used to convert could be calculated by the area between the cutting curve the bitmap into a vector graph for extracting the contours of and the displacement axis [22]. the geometrical features of the teeth of the cricket. To easily When the loading speed was 10 mm/s with a cutting force separate the object from the background of the image, the of 2.5 N, the cross-section of the tea stalk was changed. More- over, X-ray microcomputed tomography (Scanco Medical vector graph was subjected to a binary process and was con- verted into a black-and-white image. Also, AutoCAD soft- AG, micro-CT 100, Switzerland) was used to scan the tested ware was used to adjust and plot the points to extract the stalks after the cutting experiment. The X-ray tube had a spot contour line of the serrated structure on the mandible of size of 5 mm with an operating voltage of 45 kV and a current the cricket. The curve of the outer margin of the serrated of 88 μA. A total of 200 sliced images (each with 1024 × 1024 pixels) were obtained from the experiment. The tea stalk was structure was divided into individual curves to precisely y (pixel) y (pixel) 63° 27° 4 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 5: Cutter models: (a) a, (b) b, (c) c, and (d) d. fixed on a sponge in the scanning barrel to observe its inter- nal structure. 3. Results and Discussion 3.1. Curve of the Tooth Structure. The teeth on the mandible of the cricket varied in terms of size and shape. Different arc- shaped structures of the teeth significantly reduced the fric- tional resistance between the mandible and the new shoots Figure 6: Angles of the triangle. of the plant. is presented in the following equation: 3.1.1. Fitting Curve of the Serrated Structure. The arc-shaped structure of the teeth on the mandible of the cricket was 2 3 yx =0:16166 + 2:61437x +0:0356x − 0:00562x − 2:61 ðÞ divided into five curves (curves a–e). A nonlinear regression −6 4 −6 5 model was used to analyze the outer margin of curves a to e. ×10 x +2:02 × 10 x : The fitting of the curve of the serrated structure is given in the ð2Þ following equation: When the fitted straight line was used, curve a was fitted 2 3 4 by the least squares method. The fitting function was set as in yxðÞ = a + a x + a x + a x + a x : ð1Þ 0 1 2 3 4 the following equation: SxðÞ = b + b x: ð3Þ The fitting parameters of the tooth curve are presented in 0 1 Table 1. It was found that the values of R for all curves (a, b, c, d, and e) were greater than 0.9595. Therefore, the results of The least squares method was used for the rising and fall- ing parts of the curve (Figure 4). The fitting parameters b fitting were acceptable. Figure 2 shows curves a–e. Curves a, and b were calculated using Origin software, as shown in c, and e had the same trend of rise and fall, whereas curves b Table 2. The slopes of the rising and falling parts on the and d had slightly different ones. Curve a increased almost approximate line segment were 1.959 and –1.891, respec- linearly while curves c and e were convex in their rising parts before decreasing. The peak value of curve a was larger than tively. In the Cartesian coordinate system, the corresponding ° ° those of the other curves. dip angles were 63 and 118 , with corresponding R values of 0.964 and 0.953. These results indicated a high correlation between the fitted line and the true curve. 3.1.2. Best Approximation of the Fitting Curve. The first sharp Therefore, the fitting curve and straight lines could tooth (Figure 1(a)) on the mandible of the cricket cuts off the replace the curve of the profile of the first tooth on the man- shoots efficiently, and the other teeth are used to grind the dible of the cricket for simplifying the processing technology food [30, 34]. The first sharp tooth can reduce the cutting and retaining bionic characteristics. resistance as well. Curve a, which models this tooth, was thus selected to design the model of the cutter. 3.1.3. Cutter Design and Manufacture. Different cutters with To reduce the difficulty of processing the cutter, curve a no burrs on the corners are shown in Figure 5. Cutter a was a was replaced by the fitted curve and straight lines to simplify traditional cutter used for a comparison of cutting perfor- the shape of the tooth while retaining its bionic characteris- mance with the other cutters—b, c, and d—which were bio- tics. In the fitted curve (and straight line), the sum of squares mimetic. They were designed based on the curve of the of the error was used as the optimum index to seek the best- structure of the first sharp tooth on the mandible of the matching function. When the fitted curve was used, the cricket (i.e., curve a). The contour line of cutter a was trape- expression of curve a was a five-order polynomial equation zoidal. Those of cutters b and c were the fitted curve of Equa- with an R value of 0.999 (Figure 3). The fitting of the curve tion (2) and the fitted scalene triangle of Equation (3), 28° 62° Applied Bionics and Biomechanics 5 3.5 0.06 0.05 2.5 0.04 0.03 1.5 0.02 0.01 0.5 1.5 1.75 2 2.25 2.5 1.5 1.75 2 2.25 2.5 Cutter thickness (mm) Cutter thickness (mm) Cutter a Cutter c Cutter a Cutter c Cutter b Cutter d Cutter b Cutter d (a) Equivalent stress (b) Total deformation Figure 7: Rule of equivalent stress and total deformation of the cutter with thickness. Table 3: Maximum force during the cutting of the tea stalk. Maximum cutting force (N) Loading speed No. Cutter Cutter Cutter Cutter (mm/s) 10 a b c d 1 10.578 9.640 9.353 8.446 2 8.004 9.047 8.749 6.589 3 5 8.008 9.280 8.609 7.783 4 8.500 9.020 9.020 11.365 Cutter a Cutter b Cutter c Cutter d 5 10.338 8.249 9.206 11.791 Loading speed of 5 mm/s 1 9.834 9.884 9.857 11.659 Loading speed of 10 mm/s 2 8.039 7.369 9.729 12.225 Loading speed of 15 mm/s 3 10 11.574 9.311 8.997 10.516 Figure 8: Average maximum cutting force. 4 8.334 9.008 7.594 12.245 5 8.811 10.392 8.958 8.051 mum equivalent stresses produced by cutters b and c were 1 7.756 9.582 7.896 12.497 similar and lower than those produced by cutters a and d. With an increase in the cutter thickness, its total deforma- 2 10.694 7.407 8.004 11.330 tion decreased gradually. The trend of change in cutter a 3 15 9.458 7.853 8.683 14.726 was prominent, whereas those of cutters b, c, and d went 4 8.566 7.524 9.132 14.477 smoothly. When the thickness of the cutter was 5 8.632 8.489 8.667 14.954 1.5~2.5 mm, the maximum equivalent stress and total deformation produced by cutters b and c did not change significantly with thickness. respectively. The contour line of cutter d was a combination of a trapezoid and a scalene triangle. For cutters c and d, the angles of the two sides of the triangle along the vertical 3.3. Experiment to Test Cutting Performance ° ° direction were 27 and 28 , respectively (Figure 6). 3.3.1. Cutting Force. The cutting force reflects the efficiency of 3.2. Analysis of the Cutter Thickness. Stress and deformation cutting. To clearly examine the efficiency of the cutter, the had a significant influence on the stability and wear of the maximum cutting force at loading speeds of 5, 10, and cutter. Many factors in turn affect the stress and deformation 15 mm/s was used (Table 3). The average maximum cutting of the cutter, such as its mechanical properties, type of cutter, force is shown in Figure 8. and structural and motion-related parameters. The authors At a loading speed of 5 mm/s, the average maximum here examined the influence of the thickness of the cutter forces of cutters a, b, c, and d were 9.086 N, 10.047 N, on the stress on it and its deformation. 8.987 N, and 9.195 N, respectively (Table 3 and Figure 8). Assuming that the load was 3 N, the finite element The average maximum cutting forces of cutters b and d analysis showed that the stress field and deformation of increased by 10.58% and 1.2%, respectively, compared with that of cutter a. However, the average maximum cutting force the cutter changed with its thickness, as shown in Figure 7. The maximum equivalent stress of the cutter of cutter c was smaller than that of cutter a by 1.08%. The decreased first and then changed a little with increasing average maximum cutting forces of cutters b, c, and d were thickness. At different thicknesses of the cutter, the maxi- 9.193 N, 9.027 N, and 10.939 N, respectively, at a loading Equivalent stress (MPa) Total deformation (mm) Average cutting force (N) 6 Applied Bionics and Biomechanics degrees, and the cutting times and energies consumed by dif- Table 4: Energy consumed to cut a single tea stalk. ferent cutters were different. Energy consumption (J) Loading speed No. Cutter Cutter Cutter Cutter (mm/s) 3.3.2. Energy Consumption. Energy consumption is an a b c d important factor that reflects the efficiency of cutting. It can 1 1.717 1.059 1.122 1.638 be represented by the area between the curve of the cutting 2 1.123 1.216 0.996 1.122 force and the displacement axis [21]. When the loading speeds were 5, 10, and 15 mm/s, the energy consumed by 3 5 1.025 1.068 1.087 1.345 the different cutters is recorded in Table 4 and their average 4 0.745 1.284 1.318 1.642 energy consumption is shown in Figure 9. 5 1.219 1.272 1.266 1.756 At loading speeds of 5 and 10 mm/s, the average energy 1 0.920 1.023 0.929 1.491 consumption of cutter d was higher than those of the other 2 1.149 1.358 1.154 1.933 cutters (Table 4 and Figure 9). The average maximum cutting 3 10 1.058 1.255 1.207 2.445 forces of cutters a, b, and c were similar. When the loading speed was 15 mm/s, the average energies consumed by cut- 4 1.298 1.185 1.318 2.649 ters a, b, c, and d were 1.225 J, 1.056 J, 1.173 J, and 2.567 J, 5 1.354 1.256 1.148 1.442 respectively. Compared with cutter a, the average maximum 1 1.205 1.373 0.958 2.281 cutting forces of cutters b and c were smaller by 13.8% and 2 1.499 1.019 1.163 2.936 4.24%, respectively, whereas that of cutter d was larger by 109.55%. 3 15 1.356 1.009 1.277 2.843 The energy consumed by the biomimetic cutters b and c 4 1.183 1.035 1.173 2.293 were lower than those consumed by the traditional cutter a 5 0.882 0.843 1.293 2.481 and the biomimetic cutter d. 4. Discussion 2.5 4.1. Behavior Mechanism of Crickets. The studies had shown that insects could decide which angle to eat and when best to 1.5 fight by the powers of neuromodulation [29]. With the genetic techniques, the neuron which influenced aggression had been found in the fruit fly. In crickets, though, we knew 0.5 nothing about the neuron of the eat and fight. In addition, there were few studies on the effects of left-right asymmetries Cutter a Cutter b Cutter c Cutter d in the brain and behavior on crickets (invertebrates) when eating and fighting [36]. Therefore, further research is Loading speed of 5 mm/s needed on the working mechanisms allowing left-right man- Loading speed of 10 mm/s dible bite behavior in crickets. This might be due to the differ- Loading speed of 15 mm/s ence in nervous innervation. Now that the genetic techniques Figure 9: Average energy consumption at different loading speeds. are becoming available for crickets [37], it could be expected that more advances will occur in the future studies of the model system of crickets. speed of 10 mm/s, smaller by 1.35% and 3.13% and larger by 17.4%, respectively, than that of cutter a (9.318 N). The aver- 4.2. Cutting Mechanism of the Stalk. Images of structural age maximum cutting forces of cutters a, b, c, and d were changes to the tea stalk were observed using a micro-CT 9.021 N, 8.171 N, 8.476 N, and 13.597 N, respectively, when scanner and are shown in Figure 10. According to Figures 2 the loading speed was 15 mm/s. In comparison with the aver- and 9, the structure of the tea stalk can be divided into four age maximum cutting force of cutter a, those of cutters b and parts: the pith, xylem, phloem, and epidermis. A similar tis- c were smaller by 9.43% and 6.04%, respectively, whereas that sue structure was obtained by Li and Lai, who observed the of cutter d was larger by 50.72%. With the increase in loading microstructure of the tea stalk using a scanning electron speed, the average maximum cutting forces of cutters a, b, microscope [38]. Within the structure of the tea stalk, the and c showed no significant changes while that of cutter d cutting force and energy needed for the pith were low. Hence, increased. it was ignored owing to the heterogeneous nature of the tea The maximum cutting force used for the tea stalk was stalk and its softer, spongy internal structure. much higher than the general picking force of 2.59 N [35] In Figures 10(b) and 10(c), the compressive deformation because the cutters were made of Future 8000 resin, not steel. in the tea stalk before damage is shown. The xylem structure This also affected the time and energy needed for cutting. The was damaged in the compression stage. The process of cut- cutting time and energy consumption are closely related to ting the tea stalk can be divided into two stages. In the first the structural parameters of the cutter. Because of differences stage, the cutting force was applied to the xylem, which is in cutter shapes, the tea stalk was squeezed to varying the tissue supporting the plant. The second stage involved Average energy consumption (J) Applied Bionics and Biomechanics 7 (a) (b) (c) Figure 10: Structure of the tea stalk obtained through a micro-CT scanner. (a) Initial stalk. (b) Distorted stalk. (c) Damaged stalk. tion. Further work in the area should also investigate the advantages of biomimetic cutters for different crops and at different loading speeds. 5. Conclusions In this study, it was found that the cutting performance of cutters b and c was superior to that of cutter a at loading speeds of 5, 10, and 15 mm/s. Cutters b and c can use 9.43% Displacement (mm) and 6.04% less average maximum cutting force than cutter a, respectively, and required 13.8% and 4.24% less average Figure 11: Cutting force versus displacement. energy at a loading speed of 15 mm/s. When the thickness of the cutter was 1.5~2 mm, the maximum equivalent stress and total deformation produced by cutters b and c did not the application of the cutting force to the epidermis and change significantly. These results show that the first sharp phloem, which are the mechanical tissues of the tea stalk. The epidermis and xylem caused the two peaks to appear in tooth of the mandible of the cricket can be used to design bio- mimetic cutters that can cut the stalks of tea plants efficiently the curve of the cutting force (Figure 11). In Figure 11, the first and second peak values are the maximum forces that in terms of the cutting force and energy consumption. broke the xylem as well as the epidermis and phloem. A sim- ilar conclusion was obtained by Leblicq et al., who studied the Data Availability deformation of the plant stalk as well as the interaction between the plant and the force. They found that the break- The raw data used to support the findings of this study are ing of the stalk can be analyzed in two consecutive phases included within the article. (ovalization and buckling) [39]. Conflicts of Interest 4.3. Comparative Analysis of the Cutter. In general, shearing is the most effective method to cut lignocellulose materials, The authors declare there are no conflicts of interest regard- such as tea stalks. When the tea stalk was cut using cutters ing the publication of this paper. a, b, and c, the contact surface of the cutters with the epider- mis of the tea stalk formed a line. This style of contact is good Acknowledgments for shearing. Cutters b and c required smaller cutting forces and energies than cutter a, which indicates that they can bet- This study was supported by the Priority Academic Program ter cut lignocellulose materials. This is because cutters b and c Development of Jiangsu Higher Education Institutions are biomimetic cutters with a special fitted curve. Figures 8 (PAPD-2018-87), the National Key R&D Program of China and 9 show that the maximum cutting force and energy con- (Grant No. 2017YFD0700300), and the Henan Provincial sumed by cutter d were higher than the other cutters. This is Department of Science and Technology Research Project because cutter d has a small structure of the projecting tooth. (No. 212102110034). The tip of the tooth of the cutter was able to easily stab the epidermis of the tea stalk but was very small, because of References which more force was required to break the tissue structure of the tea stalk. These phenomena indicate that cutters b [1] Crops/World Regions/Production Quantity from Picklists, and c (biomimetic cutters) exhibited better cutting perfor- Food and Agriculture Organization of the United Nations, mance on the tea stalk than cutters a and d. 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Design of Structural Parameters of Cutters for Tea Harvest Based on Biomimetic Methodology

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Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 8798299, 8 pages https://doi.org/10.1155/2021/8798299 Research Article Design of Structural Parameters of Cutters for Tea Harvest Based on Biomimetic Methodology 1,2 2 2 1 1 Zhe Du , Yongguang Hu , Yongzong Lu, Jing Pang, and Xinping Li College of Agricultural Equipment Engineering, Henan University of Science and Technology, Luoyang 471023, China School of Agricultural Engineering, Institute of Agricultural Engineering, Jiangsu University, Zhenjiang 212013, China Correspondence should be addressed to Yongguang Hu; deerhu@163.com Received 21 April 2021; Revised 19 June 2021; Accepted 1 July 2021; Published 23 July 2021 Academic Editor: Donato Romano Copyright © 2021 Z He Du et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Owing to their sharp teeth, crickets can eat through new shoots of the stalks of tea plants. Inspired by the special geometrical structure of the teeth of crickets, this study designed a biomimetic cutter to reduce the force and energy required to cut the stalks of tea plants. Therefore, four biomimetic cutters were considered: a, b, c, and d. Cutter a was a traditional cutter used for comparison with the other three cutters, which were biomimetic. The cutters were manufactured using 3D printing technology and assessed by a texture tester at different loading speeds (5, 10, and 15 mm/s, respectively). The results show that cutter c delivered better performance compared to cutter a at loading speeds of 5, 10, and 15 mm/s, respectively. However, at 15 mm/s loading speed, the maximum cutting forces required for cutters b and c were 9.43% and 6.04% lower, respectively, than that for cutter a (9.021 N). Similarly, the energies consumed by cutters b and c were 13.8% and 4.24% lower than that consumed by cutter a (1.225 J). In addition, cutter c delivered the best results compared to others. Based on the study results, it was concluded that the biomimetic cutters can thus help to optimize the tea harvest. 1. Introduction energy [13]. Yamasaki et al. [14] and Galedar et al. [15] performed similar research on the structural parameters of the reciprocating cutter. Shi et al. [16] established the Tea is an aromatic beverage that is consumed all over the world [1]. Tea pluckers are widely used to improve the yield 3D models of crop stalks and cutters by using response of harvesting tea plants [2, 3]. The cutter is a key component surface methodology to determine the optimal combina- of the tea plucker that has a significant influence on its cut- tion of the kinematic parameters of the cutter at a cutting ting performance and efficiency [4, 5]. Commonly used cut- speed of 1.6 m/s, cutting angle of 15 , and working speed ters in tea pluckers include the reciprocating cutter, disk of 1 m/s. cutter, and flail-type cutter. Compared with the disk and Biomimetic technology has recently been applied to opti- flail-type cutters, the reciprocating cutter has a simpler struc- mize the design of traditional agricultural machinery and to ture and a wider range of adaptations [6–8]. Besides, it is improve its energy utilization [17–20]. It combines biological important to optimize the structural parameters of the recip- principles with engineering problems for developing solu- rocating cutter to improve its cutting performance. tions. A study by Chang et al. [21] designed a biomimetic Present research on the optimal design of the recipro- stubble cutter by imitating the outer contour of the foreclaws cating cutter has focused on its cutting speed, cutting of the nymph of the species Cryptotympana atrata for reduc- angle, geometry, and size. The mechanical properties of ing the cutting resistance. By considering the serrated inci- the plant have also been considered in the design of the sors of a grasshopper, Jia et al. [22] designed and cutter [9–12]. To design a harvesting element, a study by manufactured a biomimetic cutter to reduce the requirement Sunil et al. studied the mechanical properties of energy- of the maximum cutting force and cutting energy. Tong et al. cane stalks and found that the oblique angle and cutting [23] optimized a stubble-cutting disk based on the dynamics speed of the cutter had a significant effect on the cutting of the clawed toes of a mole rat as it digs the ground. Research 2 Applied Bionics and Biomechanics First sharp tooth Second sharp tooth Other teeth (a) (b) Figure 1: (a) Teeth on the mandible of the cricket. (b) Structure of the tea stalk. Table 1: Parameters of the curve. Parameters Curve a Curve b Curve c Curve d Curve e 3.248 –7.302 1283.896 41225.250 –16145.526 5.295 1.689 –32.294 –420.6120 107.581 0.104 –0.018 0.249 1.602 –0.263 a 7:08e − 05 –7:58e − 04 –2:70e − 03 2:83e − 04 –0.006 a 5:30e − 05 –1:04e − 07 8:00e − 07 1:69e − 06 –1:13e − 07 0.976 0.999 0.960 0.985 0.976 Curve a Curve b Curve c Curve d Curve e Figure 2: Extracted contour line of the teeth of the cricket. optimize the parameters of a cutter. For the aggression of the mouth structure to be adaptive, insects must decide what angle is best to eat. How it is done is arguably best understood in crickets (Orthoptera: Gryllidae) [29]. The cricket is an omnivorous insect that consumes the fresh shoots, stalks, leaves, and seeds of tea plants, vegetables, and other crops. The teeth in its mandible have evolved and adapted so that they can easily cut into and tear plant fibers [30]. Therefore, features of the teeth of the mandible of the cricket can be used to design an efficient cutter for tea plants. Based on the above discussion, the present paper exam- ines the structural parameters of cutters for harvesting tea plants based on biomimetic technology. The line of the outer 0 5 10 15 20 25 30 35 x (pixel) contour of the serrated structure on the mandible of the cricket is extracted, and its fitted curve was applied to design Figure 3: Best approximation of the fitted curve. a biomimetic cutter. In addition, four cutters (a, b, c, and d) were manufactured by using 3D printing technology, and experiments were carried out on a texture tester to investigate in bionics can be consulted to design a cutter that can their performance in terms of the required cutting force and reduce the energy and the cutting force needed for har- energy. Finally, the cross-section of the tea stalk was observed vesting [24, 25]. by using a microcomputed tomography (micro-CT) scanner Biomimetic cutting techniques are usually based on the to analyze the performance of the cutters. characteristics of phytophagous insects, such as the tiger bee- tle [26], bamboo weevil larva [27], and locust [28]. These 2. Materials and Methods insects have well-formed, strong mandibles to efficiently chew plants. Features of parts of their mouth can be used to 2.1. Cutter Design y (pixel) Applied Bionics and Biomechanics 3 14 16 18 20 22 24 26 28 30 32 34 0 2 46 8 10 12 14 16 18 x (pixel) x (pixel) Fitting data Fitting data Best approximation Best approximation (a) (b) Figure 4: Best approximation of the fitted straight line: (a) rising portion and (b) falling portion. express them at a given time. Finally, Origin software was Table 2: Parameters of the fitted straight line. used for data analysis to select the biomimetic units. Part b b R 0 1 2.1.4. Cutter Manufacture. The contours of the geometrical Rising portion 2.387 1.959 0.964 features of the teeth of the cricket were used in the design Falling portion 64.129 -1.891 0.953 of biomimetic cutters. To accurately express the biomimetic element, 3D printing was used to machine the cutter by using Future 8000 resin. It has a highly precise and smooth surface 2.1.1. Sample Preparation. For the present experiment, the and delivers a similar mechanical performance to that of adult crickets were collected from the suburbs of Ningyang acrylonitrile butadiene styrene (ABS). The 3D printed cutters city in Shandong Province, China. Five samples were narco- were used in all tests. Besides, the cutter material was still tized by 99% ether, and their teeth were taken out using twee- Future 8000 resin in the simulation test. zers and washed with distilled water. However, the tea samples were obtained from the Maichun Tea Farm in 2.2. Test Methods. The cutters used in the experiments were Danyang, Jiangsu, near the Yangtze River region (latitude 1.5~2.5 mm thick. Finite element analysis using ANSYS soft- ° ° ′ ′ 32 02 N, longitude 119 67 E). The experiment selected verity ware was carried out to determine the influence of the cutter tea, and the tea stalk was the third internode of the Zhongcha thickness on the cutting force. 108 variety. At the time of the sampling, the average moisture A texture tester (Stable Micro Systems, TA-XT2i) was content of the tea stalk was 73.8% (wet basis), and the picking used to measure, record, and analyze the cutting perfor- time was June 2019 [31]. mance (cutting force and time and energy consumed) of dif- ferent cutters on a tea stalk [32]. The tester had a wide range 2.1.2. Sample Observation. The geometric structure of the of moving distances of 0.1 mm–295 mm, and its accuracy of teeth of the crickets and the microstructure of the tea stalk force measurement was 0.025% at a speed of 0.1~20 mm/s. were observed by a digital microsystem (VHX-900F, KEY- The loading speed is an important factor because the tea stalk ENCE, Japan). This system was used to measure the 2D size was made of viscoelastic material [33]. In the cutting experi- and 3D outline of these objects. A photograph of the teeth on ments, the loading speeds were set to 5, 10, and 15 mm/s, the mandible of the cricket is shown in Figure 1(a), and the respectively. When the cutter was cutting the tea stalk at a structure of the tea stalk is shown in Figure 1(b). constant speed, the cutting force-displacement curve could be obtained with the texture tester. The energy consumed 2.1.3. Curve Extraction. TRACE software was used to convert could be calculated by the area between the cutting curve the bitmap into a vector graph for extracting the contours of and the displacement axis [22]. the geometrical features of the teeth of the cricket. To easily When the loading speed was 10 mm/s with a cutting force separate the object from the background of the image, the of 2.5 N, the cross-section of the tea stalk was changed. More- over, X-ray microcomputed tomography (Scanco Medical vector graph was subjected to a binary process and was con- verted into a black-and-white image. Also, AutoCAD soft- AG, micro-CT 100, Switzerland) was used to scan the tested ware was used to adjust and plot the points to extract the stalks after the cutting experiment. The X-ray tube had a spot contour line of the serrated structure on the mandible of size of 5 mm with an operating voltage of 45 kV and a current the cricket. The curve of the outer margin of the serrated of 88 μA. A total of 200 sliced images (each with 1024 × 1024 pixels) were obtained from the experiment. The tea stalk was structure was divided into individual curves to precisely y (pixel) y (pixel) 63° 27° 4 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 5: Cutter models: (a) a, (b) b, (c) c, and (d) d. fixed on a sponge in the scanning barrel to observe its inter- nal structure. 3. Results and Discussion 3.1. Curve of the Tooth Structure. The teeth on the mandible of the cricket varied in terms of size and shape. Different arc- shaped structures of the teeth significantly reduced the fric- tional resistance between the mandible and the new shoots Figure 6: Angles of the triangle. of the plant. is presented in the following equation: 3.1.1. Fitting Curve of the Serrated Structure. The arc-shaped structure of the teeth on the mandible of the cricket was 2 3 yx =0:16166 + 2:61437x +0:0356x − 0:00562x − 2:61 ðÞ divided into five curves (curves a–e). A nonlinear regression −6 4 −6 5 model was used to analyze the outer margin of curves a to e. ×10 x +2:02 × 10 x : The fitting of the curve of the serrated structure is given in the ð2Þ following equation: When the fitted straight line was used, curve a was fitted 2 3 4 by the least squares method. The fitting function was set as in yxðÞ = a + a x + a x + a x + a x : ð1Þ 0 1 2 3 4 the following equation: SxðÞ = b + b x: ð3Þ The fitting parameters of the tooth curve are presented in 0 1 Table 1. It was found that the values of R for all curves (a, b, c, d, and e) were greater than 0.9595. Therefore, the results of The least squares method was used for the rising and fall- ing parts of the curve (Figure 4). The fitting parameters b fitting were acceptable. Figure 2 shows curves a–e. Curves a, and b were calculated using Origin software, as shown in c, and e had the same trend of rise and fall, whereas curves b Table 2. The slopes of the rising and falling parts on the and d had slightly different ones. Curve a increased almost approximate line segment were 1.959 and –1.891, respec- linearly while curves c and e were convex in their rising parts before decreasing. The peak value of curve a was larger than tively. In the Cartesian coordinate system, the corresponding ° ° those of the other curves. dip angles were 63 and 118 , with corresponding R values of 0.964 and 0.953. These results indicated a high correlation between the fitted line and the true curve. 3.1.2. Best Approximation of the Fitting Curve. The first sharp Therefore, the fitting curve and straight lines could tooth (Figure 1(a)) on the mandible of the cricket cuts off the replace the curve of the profile of the first tooth on the man- shoots efficiently, and the other teeth are used to grind the dible of the cricket for simplifying the processing technology food [30, 34]. The first sharp tooth can reduce the cutting and retaining bionic characteristics. resistance as well. Curve a, which models this tooth, was thus selected to design the model of the cutter. 3.1.3. Cutter Design and Manufacture. Different cutters with To reduce the difficulty of processing the cutter, curve a no burrs on the corners are shown in Figure 5. Cutter a was a was replaced by the fitted curve and straight lines to simplify traditional cutter used for a comparison of cutting perfor- the shape of the tooth while retaining its bionic characteris- mance with the other cutters—b, c, and d—which were bio- tics. In the fitted curve (and straight line), the sum of squares mimetic. They were designed based on the curve of the of the error was used as the optimum index to seek the best- structure of the first sharp tooth on the mandible of the matching function. When the fitted curve was used, the cricket (i.e., curve a). The contour line of cutter a was trape- expression of curve a was a five-order polynomial equation zoidal. Those of cutters b and c were the fitted curve of Equa- with an R value of 0.999 (Figure 3). The fitting of the curve tion (2) and the fitted scalene triangle of Equation (3), 28° 62° Applied Bionics and Biomechanics 5 3.5 0.06 0.05 2.5 0.04 0.03 1.5 0.02 0.01 0.5 1.5 1.75 2 2.25 2.5 1.5 1.75 2 2.25 2.5 Cutter thickness (mm) Cutter thickness (mm) Cutter a Cutter c Cutter a Cutter c Cutter b Cutter d Cutter b Cutter d (a) Equivalent stress (b) Total deformation Figure 7: Rule of equivalent stress and total deformation of the cutter with thickness. Table 3: Maximum force during the cutting of the tea stalk. Maximum cutting force (N) Loading speed No. Cutter Cutter Cutter Cutter (mm/s) 10 a b c d 1 10.578 9.640 9.353 8.446 2 8.004 9.047 8.749 6.589 3 5 8.008 9.280 8.609 7.783 4 8.500 9.020 9.020 11.365 Cutter a Cutter b Cutter c Cutter d 5 10.338 8.249 9.206 11.791 Loading speed of 5 mm/s 1 9.834 9.884 9.857 11.659 Loading speed of 10 mm/s 2 8.039 7.369 9.729 12.225 Loading speed of 15 mm/s 3 10 11.574 9.311 8.997 10.516 Figure 8: Average maximum cutting force. 4 8.334 9.008 7.594 12.245 5 8.811 10.392 8.958 8.051 mum equivalent stresses produced by cutters b and c were 1 7.756 9.582 7.896 12.497 similar and lower than those produced by cutters a and d. With an increase in the cutter thickness, its total deforma- 2 10.694 7.407 8.004 11.330 tion decreased gradually. The trend of change in cutter a 3 15 9.458 7.853 8.683 14.726 was prominent, whereas those of cutters b, c, and d went 4 8.566 7.524 9.132 14.477 smoothly. When the thickness of the cutter was 5 8.632 8.489 8.667 14.954 1.5~2.5 mm, the maximum equivalent stress and total deformation produced by cutters b and c did not change significantly with thickness. respectively. The contour line of cutter d was a combination of a trapezoid and a scalene triangle. For cutters c and d, the angles of the two sides of the triangle along the vertical 3.3. Experiment to Test Cutting Performance ° ° direction were 27 and 28 , respectively (Figure 6). 3.3.1. Cutting Force. The cutting force reflects the efficiency of 3.2. Analysis of the Cutter Thickness. Stress and deformation cutting. To clearly examine the efficiency of the cutter, the had a significant influence on the stability and wear of the maximum cutting force at loading speeds of 5, 10, and cutter. Many factors in turn affect the stress and deformation 15 mm/s was used (Table 3). The average maximum cutting of the cutter, such as its mechanical properties, type of cutter, force is shown in Figure 8. and structural and motion-related parameters. The authors At a loading speed of 5 mm/s, the average maximum here examined the influence of the thickness of the cutter forces of cutters a, b, c, and d were 9.086 N, 10.047 N, on the stress on it and its deformation. 8.987 N, and 9.195 N, respectively (Table 3 and Figure 8). Assuming that the load was 3 N, the finite element The average maximum cutting forces of cutters b and d analysis showed that the stress field and deformation of increased by 10.58% and 1.2%, respectively, compared with that of cutter a. However, the average maximum cutting force the cutter changed with its thickness, as shown in Figure 7. The maximum equivalent stress of the cutter of cutter c was smaller than that of cutter a by 1.08%. The decreased first and then changed a little with increasing average maximum cutting forces of cutters b, c, and d were thickness. At different thicknesses of the cutter, the maxi- 9.193 N, 9.027 N, and 10.939 N, respectively, at a loading Equivalent stress (MPa) Total deformation (mm) Average cutting force (N) 6 Applied Bionics and Biomechanics degrees, and the cutting times and energies consumed by dif- Table 4: Energy consumed to cut a single tea stalk. ferent cutters were different. Energy consumption (J) Loading speed No. Cutter Cutter Cutter Cutter (mm/s) 3.3.2. Energy Consumption. Energy consumption is an a b c d important factor that reflects the efficiency of cutting. It can 1 1.717 1.059 1.122 1.638 be represented by the area between the curve of the cutting 2 1.123 1.216 0.996 1.122 force and the displacement axis [21]. When the loading speeds were 5, 10, and 15 mm/s, the energy consumed by 3 5 1.025 1.068 1.087 1.345 the different cutters is recorded in Table 4 and their average 4 0.745 1.284 1.318 1.642 energy consumption is shown in Figure 9. 5 1.219 1.272 1.266 1.756 At loading speeds of 5 and 10 mm/s, the average energy 1 0.920 1.023 0.929 1.491 consumption of cutter d was higher than those of the other 2 1.149 1.358 1.154 1.933 cutters (Table 4 and Figure 9). The average maximum cutting 3 10 1.058 1.255 1.207 2.445 forces of cutters a, b, and c were similar. When the loading speed was 15 mm/s, the average energies consumed by cut- 4 1.298 1.185 1.318 2.649 ters a, b, c, and d were 1.225 J, 1.056 J, 1.173 J, and 2.567 J, 5 1.354 1.256 1.148 1.442 respectively. Compared with cutter a, the average maximum 1 1.205 1.373 0.958 2.281 cutting forces of cutters b and c were smaller by 13.8% and 2 1.499 1.019 1.163 2.936 4.24%, respectively, whereas that of cutter d was larger by 109.55%. 3 15 1.356 1.009 1.277 2.843 The energy consumed by the biomimetic cutters b and c 4 1.183 1.035 1.173 2.293 were lower than those consumed by the traditional cutter a 5 0.882 0.843 1.293 2.481 and the biomimetic cutter d. 4. Discussion 2.5 4.1. Behavior Mechanism of Crickets. The studies had shown that insects could decide which angle to eat and when best to 1.5 fight by the powers of neuromodulation [29]. With the genetic techniques, the neuron which influenced aggression had been found in the fruit fly. In crickets, though, we knew 0.5 nothing about the neuron of the eat and fight. In addition, there were few studies on the effects of left-right asymmetries Cutter a Cutter b Cutter c Cutter d in the brain and behavior on crickets (invertebrates) when eating and fighting [36]. Therefore, further research is Loading speed of 5 mm/s needed on the working mechanisms allowing left-right man- Loading speed of 10 mm/s dible bite behavior in crickets. This might be due to the differ- Loading speed of 15 mm/s ence in nervous innervation. Now that the genetic techniques Figure 9: Average energy consumption at different loading speeds. are becoming available for crickets [37], it could be expected that more advances will occur in the future studies of the model system of crickets. speed of 10 mm/s, smaller by 1.35% and 3.13% and larger by 17.4%, respectively, than that of cutter a (9.318 N). The aver- 4.2. Cutting Mechanism of the Stalk. Images of structural age maximum cutting forces of cutters a, b, c, and d were changes to the tea stalk were observed using a micro-CT 9.021 N, 8.171 N, 8.476 N, and 13.597 N, respectively, when scanner and are shown in Figure 10. According to Figures 2 the loading speed was 15 mm/s. In comparison with the aver- and 9, the structure of the tea stalk can be divided into four age maximum cutting force of cutter a, those of cutters b and parts: the pith, xylem, phloem, and epidermis. A similar tis- c were smaller by 9.43% and 6.04%, respectively, whereas that sue structure was obtained by Li and Lai, who observed the of cutter d was larger by 50.72%. With the increase in loading microstructure of the tea stalk using a scanning electron speed, the average maximum cutting forces of cutters a, b, microscope [38]. Within the structure of the tea stalk, the and c showed no significant changes while that of cutter d cutting force and energy needed for the pith were low. Hence, increased. it was ignored owing to the heterogeneous nature of the tea The maximum cutting force used for the tea stalk was stalk and its softer, spongy internal structure. much higher than the general picking force of 2.59 N [35] In Figures 10(b) and 10(c), the compressive deformation because the cutters were made of Future 8000 resin, not steel. in the tea stalk before damage is shown. The xylem structure This also affected the time and energy needed for cutting. The was damaged in the compression stage. The process of cut- cutting time and energy consumption are closely related to ting the tea stalk can be divided into two stages. In the first the structural parameters of the cutter. Because of differences stage, the cutting force was applied to the xylem, which is in cutter shapes, the tea stalk was squeezed to varying the tissue supporting the plant. The second stage involved Average energy consumption (J) Applied Bionics and Biomechanics 7 (a) (b) (c) Figure 10: Structure of the tea stalk obtained through a micro-CT scanner. (a) Initial stalk. (b) Distorted stalk. (c) Damaged stalk. tion. Further work in the area should also investigate the advantages of biomimetic cutters for different crops and at different loading speeds. 5. Conclusions In this study, it was found that the cutting performance of cutters b and c was superior to that of cutter a at loading speeds of 5, 10, and 15 mm/s. Cutters b and c can use 9.43% Displacement (mm) and 6.04% less average maximum cutting force than cutter a, respectively, and required 13.8% and 4.24% less average Figure 11: Cutting force versus displacement. energy at a loading speed of 15 mm/s. When the thickness of the cutter was 1.5~2 mm, the maximum equivalent stress and total deformation produced by cutters b and c did not the application of the cutting force to the epidermis and change significantly. These results show that the first sharp phloem, which are the mechanical tissues of the tea stalk. The epidermis and xylem caused the two peaks to appear in tooth of the mandible of the cricket can be used to design bio- mimetic cutters that can cut the stalks of tea plants efficiently the curve of the cutting force (Figure 11). In Figure 11, the first and second peak values are the maximum forces that in terms of the cutting force and energy consumption. broke the xylem as well as the epidermis and phloem. A sim- ilar conclusion was obtained by Leblicq et al., who studied the Data Availability deformation of the plant stalk as well as the interaction between the plant and the force. They found that the break- The raw data used to support the findings of this study are ing of the stalk can be analyzed in two consecutive phases included within the article. (ovalization and buckling) [39]. Conflicts of Interest 4.3. Comparative Analysis of the Cutter. In general, shearing is the most effective method to cut lignocellulose materials, The authors declare there are no conflicts of interest regard- such as tea stalks. When the tea stalk was cut using cutters ing the publication of this paper. a, b, and c, the contact surface of the cutters with the epider- mis of the tea stalk formed a line. This style of contact is good Acknowledgments for shearing. Cutters b and c required smaller cutting forces and energies than cutter a, which indicates that they can bet- This study was supported by the Priority Academic Program ter cut lignocellulose materials. 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Applied Bionics and BiomechanicsHindawi Publishing Corporation

Published: Jul 23, 2021

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