| In addition to being used as oil,rapeseed crops have been exploited and utilized for feeding,vegetable,fertilizer,flower and honey.Because of high moisture content and variable biomass of fodder rapeseed,there is a lack of applicable harvesting machinery.A fodder rapeseed harvester,suitable for small plot management mode,was developed based on the biological characteristics of fodder rapeseed plant which was thick,tall,crisp and tender.The basic structure,working process and technological route of the harvester were determined.In order to realize the sliding cutting of material and saving effort in the cutting process,a cylinder-type chopping device with herringbone arrangement of blades and a flail-type chopping device with staggered arrangement of blades were proposed.The results analysis of the comparative test-bench experiments was carried out to determine that the performance of the cylinder-type chopper was better.The numerical simulation model of the cylinder-type chopper was established,and the reason why the performance of the chopping device was affected by the dragging of the movable blades was further analyzed.An adaptive adjusting feeding mechanism was proposed,and its structure and operation parameters were improved and optimized.The feeding rate of the harvester for fodder rapeseed fluctuated greatly during the harvesting process,resulting in large load changes of each component and causing vibration of the frame.In order to reduce the vibration of the frame and avoid resonance,the dynamic performance of harvester frame was improved by combining finite element simulation test with model test.The research in more detail included:(1)The main fodder rapeseed varieties in the middle and lower reaches of the Yangtze River were selected.According to the macroscopic biomass accumulation,the biomass of the fodder rapeseed was the highest at the full-bloom stage which could reach 75 000 kg/hm~2.The biomass at full-bloom stage is 40%higher than that at bolting stage and 10%higher than that at fruit pod stage.The theoretical feeding rate of the harvester was predicted as 3.98?7.57 kg/s.The average moisture content of stalks and leaves was above 80%during the whole harvest period.With the growth of fodder rapeseed,the shear force,bending load and compression load of stalk gradually increased,and reached the peak value at fruit pod stage.The maximum average shear force was 788.94 N,the maximum bending load was 435.48 N,the radial compressive load was 576.18 N,and the axial compressive load was 757.01 N.The results showed that the fodder rapeseed during the whole harvest period was crisp and tender,easy to cut and crush.The maximum sliding friction angle of the chopped material on the surface of the sheet was less than 46.13°.(2)According to the biological characteristics of fodder rapeseed and the requirements of mechanized harvesting design,the technological routes were determined.After comparing and analyzing the different schemes corresponding to each technological process,it was determined that the crawler self-propelled power chassis,telescopic finger cylinder type gather device and unilateral discharging bin were adopted.In order to reduce the cost of fodder rapeseed harvester,the modular design method was applied to realize the rapid function reconstruction.(3)The key components of fodder rapeseed harvester,including the cylinder-type chopping device,the flail type chopping device,collecting and unloading bin and telescopic finger cylinder type gather device were designed and analyzed.In order to realize the sliding cutting of material and saving effort in the cutting process,a cylinder-type chopping device with herringbone arrangement of blades and a flail-type chopping device with staggered arrangement of blades were proposed.Based on the kinematics principle of material throwing process,the spindle speed of the cylinder-type chopping device was 559?802 r/min.According to the change of the spatial position of the stalk,the process of stalk cutting was divided into cutting process of stalk,following process of broken stalk and cutting process of broken stalk.The dynamic model of the stalk cutting process in the chopping device was established,and the factors affecting the chopping performance of stalks were determined.According to the kinematics analysis of the telescopic finger,the spindle speed of the cylinder was 45 r/min.The unilateral discharging bin of double-acting cylinder was designed.The inclination angle of the bin was 50°.(4)The comparative experiments between the cylinder-type chopping device and the flail type chopping device was carried out.The average length,uniformity,energy consumption and spraying distance of chopped material were considered to be the indexes.The results showed that the average length of the chopped material by both of the chopping devices met the requirement.The uniformity of the length of the cylinder-type chopping device was better than that of the flail-type chopping device,and the average energy consumption of flail type chopping device was less than that of the cylinder-type chopping device.But the stability and reliability of the cylinder-type chopping device were better than that of the flail-type chopping device,and the throwing distance of the cylinder-type chopping device was far longer than that of the flail-type chopping device.When the feeding rate was 4?8 kg/s,the average length of material after chopping by the cylinder-type chopping device was49.91?65.64 mm,and the uniformity was 77.42?82.09%,which met the agronomic requirements of fodder rapeseed harvest.(5)Due the difference between theoretical and actual material cutting lengths,the finite element method was used to simulate and analyze the material movement during the cutting process to explore the interaction between the chopping device and the material.The Plastic?Kinematic failure model of stalk was reasonably inferred by experimental measurement and simulation.The maximum error between the simulation value and the real value of the maximum shear force is 7.59%.The numerical simulation model of the cylinder-type chopping device was established,and the reason why the performance of the chopping device was affected by the dragging of the movable blades was analyzed.In order to reduce the dragging of stalks,an adaptive feeding mechanism was proposed to change the feeding form from passive disorderly feeding to active orderly feeding.The operation parameters of the improved cylinder-type chopping device were optimized.The single factor experiment results showed that the spindle speed of feeding roller was 400?550r/min,the spindle speed of chopping was 600?800 r/min,and the qualified rate of the chopping length of stalks was better.Through the quadratic rotation orthogonal combination experiment,the qualified rate of chopping length and power consumption were 91.16%and 3.98 k J,respectively,while the feeding roller speed was 496.17 r/min and the spindle speed of the chopping device was 709.14 r/min.(6)On the basis of improving the technological route to improve the chopping performance,the vibration characteristics of the frame were analyzed to further improve the reliability and operation performance of the whole machine.The accuracy of the model was verified by the analysis of the first six modal frequencies and modes of the frame in free mode.The maximum error of natural frequencies of the two models was 7.53%.The mode shapes were basically the same,so the model was reasonable.The natural frequencies and external excitation frequencies of the frame were compared and analyzed,and the excitation sources causing the resonance of the frame were selected.The thickness of bracket material in different parts had significant influence on the natural frequency of the new frame.It had been established that the optimization model of the material thickness and quality of the new frame.The first three natural frequencies of the optimized frame were 30.068 Hz,51.479 Hz and 55.677 Hz,respectively,which avoided the external excitation frequency range and effectively avoids resonance.Field vibration test showed that the vibration of the new frame was stable,the vibration amplitude of all measuring points did not exceed 5 m/s~2,the frame had not obvious resonance,and the vibration performance of the whole machine was good.(7)The field experiments of fresh-feeding and harvesting were carried out.The qualification rate of chopping length and stubble failure rate were considered to be the indexes.The results showed that all parts of the machine were running normally,the discharging passage of the chopping device was not blocked,and the material was conveyed smoothly.The average qualified rate of chopping length was 95.92%at bolting stage,90.36%at full-bloom stage,and 88.06%at fruit pod stage.The qualified rate of chopping length met the feeding requirements of fodder rapeseed.The average stubble breakage rate of regenerated fodder rapeseed was not higher than11.17%in the suitable harvest period,and the biomass of regenerated fodder rapeseed after machine harvest was 10.9%lower than that of artificial harvest.The feeding time of fodder rapeseed harvested by machine was 35.44%shorter and the feed intake increased 33.35%on average under the same feeding rate than that harvested by artificial harvest.The average intake rate of fodder rapeseed fed by machine in different periods was 94.05%.There was no significant difference in the intake of fodder rapeseed in different periods,and the intake time was quite different.The field experiments on silage harvesting were carried out.The results showed that the moisture content of the plant decreased to less than 75%to meet the silage requirements after 4 days of cutting and drying.When the moving speed of the machine was not higher than 0.7 m/s,the qualified rate of pickup was not less than95.80%,which met the requirements of pickup and harvesting. |
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