Research On Physical And Mechanical Properties Of Headed Chinese Cabbage And Its Crawler Self-propelled Harvesting Equipment

Chinese cabbage is a kind of headed leafy vegetable of Brassica genus of cruciferous family.It is widely grown in China,with North China and the south of Yangtze River as the main producing areas.However,Chinese cabbage remains a need for manual harvesting,and the problems of high intensity,low efficiency and poor benefit have become increasingly prominent,which greatly restrict the development of Chinese cabbage industry.Therefore,mechanized harvesting is increasingly urgent in demand.In this study,the headed Chinese cabbage in Jiangsu,Zhejiang,and Shanghai,one of the major vegetable production areas in China,was taken as the research object.Based on analysis of the grow agronomic and physical and mechanical properties of Chinese cabbage,a crawler self-propelled heading Chinese cabbage harvester that integrated root cutting,clamping and guiding,and transportation devices had been developed combining simulation analysis and field trials of the prototype.In addition,the key components of the harvester were optimized,and the planting agronomic specifications suitable for mechanized harvesting was put forward to meet the high-efficiency,low-loss,and cost-saving production requirements for Chinese cabbage,and to fianally solve the key technical problems of heading Chinese cabbage harvest in southern China.The main research contents and conclusions were as follows:（1）Research on statics characteristics of Chinese Cabbage.The main physical parameters such as shape,size,apparent density,and friction coefficient of Chinese cabbage were determined,and the root cutting characteristics were tested.Moreover,the static load compression feature of Chinese cabbage was determined,and the differences of stress relaxation characteristics under different loading directions were compared from macro and micro levels.Meanwhile,the relationship between parameters of stress relaxation characteristic and quality attribute under common transverse loading conditions was also explored.Results showed that the faster the cabbage loading rate,the smaller the limit value of compression force.The intact Chinese cabbage has viscoelasticity under lower loading speed and smaller deformation,and the generalized Maxwell model could well describe the relaxation process.The upper limit of failure and deformation of transverse compression was larger than that of longitudinal compression,and the stress relaxation of transverse loading was faster than that of longitudinal loading.There were differences in cell geometry and tissue structure in different tissues of Chinese cabbage,which resulted in different rheological properties in different loading directions.The results of microstructure analysis were basically consistented with the compression and relaxation responses of Chinese cabbage under different loading directions.Differences of Chinese cabbage in different storage periods could be characterized by the first three principal components of the relaxation characteristics.The quality characteristic prediction model based on the stress relaxation characteristic parameters of Chinese cabbage showed a good fitting effect on puncture firmness and VC content.（2）Research on kinetic characteristics and damage mechanism of Chinese Cabbage.Based on the percussive vibration test,the dynamic properties of intact Chinese cabbage were analyzed,and the optimal detection location of vibration response was optimized.The influences of three different model structure composition modes on the free mode of Chinese cabbage were compared and analyzed based on ANSYS.Based on orthogonal test,the relationship between the drop impact and mechanical damage of Chinese cabbage was explored,and the primary and secondary factors affecting mechanical damage were analyzed,and the relationship between damage characteristics and vibration characteristics was explored based on LDV technology.Morever,the test conditions of compactness measurement device were also optimized based on orthogonal test,and the relationship between quality attributes and vibration characteristics of Chinese cabbage was explored based on compactness and other quality indexes introduced.Results showed that different detection methods had a certain impact on the vibration spectrum,and the system of Chinese cabbage was approximately linear at the petiole position at the equator.The three-layer package structure could effectively simulate the overall structure of Chinese cabbage.The drop impact damage of Chinese cabbage was related to the radius of curvature and the position of center of gravity.The factors that had a significant impact on the comprehensive damage index DCI of the Chinese cabbage during the drop impact process were the drop height and the contact plate material in order.The compactness index could better reflect the overall structure and texture of Chinese cabbage and was superior to traditional puncture test in overall evaluation.The mechanical vibration response method can be used to evaluate and predict the quality indicators of Chinese cabbage,and the performance of the prediction model could be improved after introducing vibration component indicators in multiple directions.（3）Design and analysis of crawler self-propelled Chinese cabbage harvester.The mechanized harvesting scheme of Chinese cabbage was determined by cutting root first,then guiding,transporting,and collecting.Based on the study of the physical and mechanical properties of Chinese cabbage,the harvester structures,initial parameter conditions and value ranges of each key component were determined.An asymmetric cutting device was designed,which was combined with a left serrated disk and a right concave disk,and the critical conditions of smooth root cutting without leakage and damage of adjacent rows of Chinese cabbage were determined.A flexible clamping guide device was designed,and the working conditions of Chinese cabbage without falling,blocking and squeezing in the process of clamping and conveying were determined.An inclined conveyer lifting device was designed and its conveyer movement process was analyzed,and the condition of Chinese cabbage without falling impact damage and rolling was determined.Finanlly,the scheme of hydraulic transmission system and the type of hydraulic motor of full-tracked Chinese cabbage harvester were determined,and the main technical parameters of chassis were calculated.（4）Simulation and optimization of key components of crawler self-propelled Chinese cabbage harvester.Based on DEM,the root cutting device of Chinese cabbage was simulated and optimized,and the combined structure of traditional cutting knife was compared and analyzed.The modal verification analysis of the cutting disk structure and the main structure of frame were carried out based on ANSYS.The clamping and guide device was simulated and optimized based on the coupling of EDEM and Recur Dyn.Results showed that there existed little difference between the maximum root cutting reaction force and original value when the cutting disc rotation speed was 187 r min^-1,cutter overlap was 18 mm,pitch angle was 12°,and forward speed was0.30 m s^-1.The root cutting process of asymmetric cutting disk structure was shorter than that of other cutting disk combinations,and the modal analysis of the two cutting disk blades confirmed the rationality of the disk structure and speed parameter settings.The proposed two-layer particle model inside and outside the root could better simulate the actual cutting process of the root,moreover,the internal and external layers of the particle structure were not consistent with each other during the root cutting process,but they were consistented with the difference in the microstructure of the root.The factors that affect the maximum clamping force of Chinese cabbage,in order of significance,were as follows:minimum ground clearance of the clamping belt,rotation speed of the clamping belt and width of the clamping belt,but the influence of the angle of the clamping belt was not significant,then the optimal parameters of the above factors were determined as 50 mm,400 r min^-1,30 mm,and 15°,respectively.（5）Research on field test and planting agronomic standards of crawler self-propelled Chinese cabbage harvester.Based on the optimized structural parameters and working parameters of each key component,a prototype of a single-row crawler self-propelled Chinese cabbage harvester was integrated and trial-produced,and the prototype field test experiment was carried out based on the proposed field operation and performance testing method.The test results showed that the productivity of harvester prototype was 0.11 hm² h^-1,the qualified root-cutting rate was 93.40%,the success rate of clamping was 95.86%,the delivery success rate was 100%,and the operation loss rate was 7.84%,indicating that the harvester proposed in this study basically has the capability of mechanized harvesting for Chinese cabbage.The agronomic planting modes of Chinese cabbage suitable for mechanized harvesting mainly include flat planting,single-row ridge planting,double-row ridge planting and wide-ridge planting.The recommended ridge spacing series were 600,900,1200,1500 and 1800 mm,and the planting row spacing was not less than450 mm,the maximum row spacing could be up to 750 mm,and the planting plant spacing was not less than 350 mm,while the maximum plant spacing could reach 500 mm.