Research On Biomimetic Design Of Cutting Blade For Tea Stem And Its Cutting Performance

Tea leaf is one of the important commercial crops in China.The traditional method of manual plucking has the disadvantage of low efficiency,lager labor,and high cost.And inadequate plucking efficiency is the main bottleneck in restricting the development of the tea industry in China.Therefore,the demand for mechanized plucking tea is urgent.In practice,mechanized plucking tea could be regarded as the interaction process of cutting blade and tea stem.To reduce the cutting resistance and energy consumption,based on the mechanical properties of tea stem,a biomimetic cutting blade which combined shape biomimetic technique with the structure and kinematic parameters of the cutting blade was designed.To reduce the number of field experiments,based on the finite element analysis,a suitable constitutive relation of tea stem and the finite element model of biomimetic cutting blade were established for the dynamic simulation of the cutting process of tea stem.At present,there are some problems such as a lack of research on the cutting mechanism,high cutting energy consumption and low cutting quality in the practical working of tea plucking machines.Because of the above problems,the mechanical properties and microstructure of tea stems were used to study the cutting mechanism.For optimizing the cutting parameters,the stem supporting way,cutting method as well as the structure and kinematic parameters of cutting blade were investigated to analyze the influence rules of the cutting performance.The cutting performance of biomimetic cutting blade is analyzed by the finite element modeling and actual cutting performance test.This study could provide a theoretical basis for the optimal design of cutting components in the tea plucking machine and the selection of working parameters.Specific research contents and results are as follows.(1)Study on microstructure and cutting properties of tea stemBy analyzing the microstructure and cutting force curve of tea stem,the results showed that the cutting properties of tea stalk were closely related to the structure of xylem and cortex.Based on the test of mechanical properties,chemical components and cutting properties of tea stem,the cutting property parameter model of tea stem was established with the grey relational analysis(GRA)+multiple linear regression(MLR).Due to the grey relational grade(GRG),the cutting property parameters(bending force and cutting force)of the stem were closely related to its mechanical property parameters(stem segment number,stem diameter,stem inter-node distance,moisture content,fracture deflection,moment of inertia,young's modulus)and chemical components(hemicellulose,cellulose,lignin).When the threshold value was 0.6 GRG,the values of the determination coefficient(R_c~2)of the correction model of bending and cutting force with GRA+MLR were 0.942 and 0.990,and the values of root-mean-square error(RMSEC)were 3.326 N and 0.257 N,respectively.(2)Study on the morphological structure of incisor lobe of cricket jaw of biomimetic objectBased on the shape serrated structure,the cricket's jaw has a good cutting performance.Its contour curve was extracted by analyzing the surface morphology of the jaw with a digital microscope.According to the second derivative and curvature of the contour curve as well as the actual working condition of the jaw's cutting,the incisor lobe of jaw was selected as a biomimetic object of cutting blade.Based on the profile curve of incisor lobe,a quintic polynomial and a linear regression equation were established,and the fitting degree was greater than 0.953.Then,scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)were used to analyze the microstructure and energy spectrum of the incisor lobe surface.The results showed that the edge surface of the jaw's incisor lobe suffered obvious abrasions,and irregular protruding points existed on the surface of the incisor lobe.The element types and contents of the surface of incisor lobe and jaw end were different.(3)Cutting analysis of tea stem and design of biomimetic cutting bladeThe sliding cutting and high speed supported cutting were determined by analyzing the influence of stem support and cutting method on cutting performance,which could reduce the cutting force and energy consumption.X-ray computed tomography was used to analyze the morphology of cutting notch on tea stem.The results showed that e maximum cross-sectional area and volume had a close relationship with the cutting force,cutting edge angle and cutting depth.When the cutting edge angle of cutting blade was35°,with the increase of cutting depths(0.7,1.5,2.3 mm),the maximum cross-sectional area ratio and volume ratio increased from 8.51%to 22.83%and from 2.98%to 5.76%,respectively.Then,based on the cutting pattern of a reciprocating cutter,the influence of tooth crest width,tooth root width,tooth height,toot pitch and cutting speed index on one cutting rate,re-cutting rate and leakage rate was analyzed by response surface method.The optimal combination of the structure and kinematic parameters of cutting blade was as follows:tooth crest width of 3.5 mm,tooth root width of 13.0 mm,tooth height of 29.0mm,toot pitch of 45.0 mm and cutting speed index of 0.8.Meanwhile,the values of one cutting rate,re-cutting rate and leakage rate were 92.60%,6.62%and 0.78%,respectively.Based on the structure parameters of cutting blade and the morphological structure of incisor lobe,four cutting blades(biomimetic cutting blade b with a quintic polynomial,triangular biomimetic cutting blade c,sawtooth biomimetic cutting blade d,and cutting blade a without biomimetic elements)were designed.(4)Finite element analysis of biomimetic cutting and experimental research on cutting performanceBased on the structural finite element analysis of cutting blade,the maximum equivalent stress,maximum equivalent strain and total deformation of biomimetic cutting blade d were larger than others.When the cutter thickness was in the range of 1.5~2.0 mm,it had no significant effect on the maximum equivalent stress and strain of biomimetic cutting blade b and c.According to the finite element simulation of biomimetic cutting analysis,the biomimetic cutting blade b and c generated the stress was 0.459 MPa and0.620 MPa,respectively.Meanwhile,the deformation of tea stem was smaller,which was0.758 mm and 0.890 mm.Then,the cutting performance test was carried out.Compared with the average cutting force of cutting blade a(9.318 N),biomimetic cutting blade b(9.193 N)and c(9.027 N)decreased by 1.35%and 3.13%,respectively,and biomimetic cutting blade d(10.939 N)increased by 17.40%when the loading speed was 10 mm/s.Besides,the average cutting energy consumption of biomimetic cutting blade c was the lowest(1.151 J),followed by cutting blade a(1.156 J)and biomimetic cutting blade b(1.5J),and finally was biomimetic cutting blade d(1.992 J).Considering the results of finite element simulation analysis and experimental research,biomimetic cutting blade b and c were more suitable for cutting tea stems than biomimetic cutting blade d.(5)Field experimental study on biomimetic cutting performanceBased on the comprehensive consideration of simulation,experimental research and blade processing technology,the cutting blade a without biomimetic elements,biomimetic cutting blade b with a quintic polynomial and triangular biomimetic cutting blade c were selected for the field experiments.The cutting quality was compared by a single factor test on the varieties of tea tree and types of cutting blade.The results showed that the intact bud-leaf rate of biomimetic cutting blade b was the highest(96.38%)and the leakage rate of biomimetic cutting blade c was the lowest(5.04%)with cutting dip angle of 0o,cutting speed of 0.64 mm/s and advance speed of 0.80 mm/s.The biomimetic cutting blade had a higher intact bud-leaf rate and lower leakage rate than these of the ordinary cutting blade.Then,the orthogonal test was carried out with the factors of cutting speed index,cutting angle and cutting blade type as influencing factors,as well as intact bud-leaf rate and leakage rate of bud and leaves as indexes.Through the intuitive analysis and the analysis of variance were obtained that the significant order of the influence of test factors on the intact bud-leaf rate and leakage rate was cutting dig angle cutting speed index and cutter type.The optimal combination is cutting speed of 0.8 mm/s,advance speed of 1.0 m/s,cutting dig angle of-3o,and biomimetic cutting blade b which will share the incisor lobe structure of cricket with a quintic polynomial.