精密播种机覆土与镇压过程对种子触土后位置控制的研究
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摘要
精密播种作业质量是由仿形、开沟、排种、覆土及镇压五个主要工作部件综合作用决定的，任何一个部件结构性能存在问题都会影响精密播种作业的整体质量。然而在以往的研究过程中，对上述五个主要工作部件的重视程度是不同的，早期精密播种技术研究主要集中在排种器能否提供均匀的种子流方面，致使排种器在精密播种机五个主要工作部件中质量与性能远远优于其它部件，技术理论也处于遥遥领先地位。直到上世纪90代以来，人们才开始逐步重视到其它主要工作部件的试验研究，使精密播种理论得到了极大的丰富与发展，精密播种机作业质量也得到了较大提高，精密播种技术得到了迅速推广。但在覆土、镇压部件与作业环节方面仍然缺乏深入系统的研究，既没有充分考虑覆土与镇压部件的类型特点、结构与运动参数的优化，也不重视覆土与镇压部件的加工质量，结果使精密播种机只实现了精密排种却未达到精密播种要求。
鉴于目前在精密播种机的研究中，关于覆土与镇压部件理论上和试验研究方面存在的问题，本文以对种子触土后土壤的运动状态、土壤压实程度影响较大的覆土器和镇压器为研究对象，对种子触土后位置和覆土厚度进行了深入、系统的研究。利用有机玻璃板制作了挤压式、双圆盘式、八字形覆土器，以及自行研制的装有压力传感器的可变力苗带镇压器，通过均匀设计设计方法及高速摄像系统等，分析了三种覆土器结构参数与运动参数对覆土过程中种子水平位移量与覆土厚度的影响；通过正交试验设计方法进行了镇压器的不同镇压力对实际播深、位移变化等影响的试验研究，并建立了相关数学模型，优化出了最佳覆土器种类和最佳结构参数与运动参数及最佳镇压力。利用LS—DYNA软件中SPH方法进行了覆土和镇压过程中土流与种子运动状态进行了仿真分析，应用Solidworks软件对精密播种机单体覆土器与镇压器进行了虚拟制造和运动仿真，提高了设计的准确性和效率，为进一步提高精密播种机设计质量和丰富精密播种理论进行了有益的探索。
本文是高等学校博士学科点专项科研基金（20040183024）和吉林省科技发展计划项目（200405045）、国家现代农业产业技术体系建设专项资金（CARS-01-33）的部分内容，其主要研究内容如下：
1、研制了八字形、双圆盘式和挤压式三种不同工作原理的新型覆土器，覆土部件的角度、高度、宽度、前后位置均可调节，便于参数优化，可实现不同条件下种子触土后位置变化的试验研究。基于Solidworks软件建立了三种覆土器与镇压器的仿真模型，利用透明有机玻璃板制成了三种覆土器，方便试验过程中对土流与种子运动状态观测。
2、基于高速摄像技术在土槽实验台上完成了三种覆土器覆土过程测试试验，利用均匀设计设计方法建立了不同条件下种子位移量和覆土厚度的回归模型，覆土器回归模型如下：
八字型覆土器种子位移量回归模型为：
回归模型表明：影响八字形覆土器种子位移量的主次因素依次为覆土器张角与机器速度的交互项、机器速度、张角与倾角的交互项，最后是张角与倾角。
八字形覆土器覆土厚度回归模型为：
回归模型表明：影响八字形覆土器覆厚度的主次因素依次为覆土器倾角、张角与倾角的交互项、张角与机器速度的交互项，最后是覆土器张角。
双圆盘式覆土器种子位移量回归模型为：
回归模型表明：影响双圆盘式覆土器种子位移量的主次因素依次为覆土器倾角和张角的交互项、张角、机器速度、倾角，最后是作业速和张角的交互项。
双圆盘式覆土器覆土厚度的回归模型为：
回归模型表明：影响双圆盘式覆土器覆土厚度的主次因素依次为覆土器张角与倾角的交互项、作业速度与张角的交互相、速度和倾角的交互项、张角、倾角，最后是作业速度。
挤压式覆土器种子位移量回归模型为：
回归模型表明，影响挤压式覆土器种子位移量的主次因素依次为速度与倾角的交互项、作业速度。
挤压式覆土器覆土厚度回归模型为：
回归模型表明：影响挤压式覆土器覆土厚度的主次因素依次为覆土器倾角、作业速度，最后是作业速度与倾角交互项。
经过对上述回归模型优化后，得出了三种覆土器的最优试验因素水平，并确定了最优覆土器为挤压式覆土器，最优试验因素水平为作业速度X1=4km/h，覆土圆盘倾角X_2=300，此时种子最小位移量为△Y_1=0.0075m，覆土厚度为△Y_2=0.0389m。
同时进行的高速摄像试验结果表明，覆土前种子位移量都很小，决定覆过程中种子位移变化的主要原因是种子被覆盖后随土流一起运动而引起的。八字形与双圆盘式覆土器覆土过程引起的土流运动剧烈，种子位移变化量大，同时覆土厚度也大；挤压式覆土器覆土过程对种床土壤扰动量很小，因此，种子的位移量小，覆土厚度适宜。
3、基于光滑粒子流体动力学方法（SPH），完成了覆土器覆土过程中土壤运动状态、种子位移量、覆土厚度和实际播深等动力学仿真，完成了土壤物理参数及力学参数的测定。仿真结果与试验结果基本吻合：八字形覆土器覆土过程种子位移量仿真与试验结果误差为△Y_1=0.002m,吻合程度为75.5%，覆土厚度误差为△Y_2=0.012m，吻合程度为80%；双圆盘式覆土器覆土过程种子位移量仿真与试验结果误差为△Y_1=0.0068m,吻合程度为71.8%，覆土厚度误差为△Y_2=0.019m,吻合程度为90.2%；挤压式覆土器覆土过程种子位移量仿真与试验结果误差为△Y_1=0.003m,吻合程度为76.6%,覆土厚度误差为△Y_2=0.003m吻合程度为89.9%，表明了利用SPH方法进行精密播种机触土部件仿真的可行性。
4、研制了一种可变力苗带镇压器，可实现镇压力由定量调节变为无级调节。利用Solidworks参数化建模软件建立了可变力苗带镇压器三维实体模型，制作了试验样机，利用S形传感器、数字显示器、计算机以及拖拉机液压元件构成镇压力测试系统，实现镇压力由定量调节变为无级调节。
5、进行了可变力苗带镇压器试验研究，系统分析了镇压力、作业速度对实际播深、种子位移量、种床土壤坚实度、出苗率、含水率及苗期植株高度的影响。结果表明：实际播深随镇压力加大而减少，其它试验指标均随镇压力的加大而提高，其中，种床土壤坚实度指标与种子位移变化量指标随着镇压力加大而增加更快，植株高度随镇压力继续加大而减小，其余试验指标则随镇压力继续加大而增加缓慢；探索了镇压力变化对种子位移量的影响，即镇压力大小对种子的粒距变化影响不大，但对覆土厚度有较大影响。镇压力对所有试验指标的影响均大于作业速度的影响。
6、利用SPH软件建立了土壤模型，基于SPH/FEM耦合算法的镇压系统LS-DYNA仿真实现。基于Solidworks参数化建模软件建立了可变力苗带镇压器三维实体模型，选取1600N～1800N镇压力和6km/h作业速度进行了镇压过程运动仿真，模型仿真结果与实际试验过程测试指标值接近，镇压器镇压过程种子实际位移与仿真位移误差为△Y_1=0.003m,吻合度为81.3%,实际覆土厚度与仿真过程获得覆土厚度误差为△Y_2=0.0017m，吻合度为96%。表明利用SPH方法对镇压器镇压过程进行仿真的方法是可行的。
本文针对精密播种机覆土器与镇压器两种触土部件的结构参数与运动参数进行了深入系统的研究，并通过SPH方法进行了动力学仿真分析，为提高精密播种机设计质量提供了新的研究法，对丰富精密精密播种理论具有重要意义。
The quality of precision seeding is comprehensively determined by theperformance of the five main working parts comprising of copying, trenching,metering, soil covering and rolling. The structure and performance issues of any partwill affect the overall quality of precision seeding operations. However, the researchon the above five parts were attached different importance in the past. A largenumber of literature data indicated that early research of precision seedingtechnology mainly focused on the ability to provide a uniform seed flow, whichresulted in the metering device’ quality and performance is superior to other parts inthe five major parts of precision seeding and its technical theory was also in theleading position. Until1990s, the experimental study of the other main workingparts has been paid more attention gradually, which developed the precision seedingtheory. The quality of precision seeding has also been greatly improved and theprecision seeding technology has gained rapid popularization subsequently.However, there is still lack thorough and systematic study in soil covering androlling parts. Neither fully considers the type characteristics, optimization of thestructure and motion parameters of soil covering and rolling parts, nor attaches moreimportance to the machining quality, which lead that precision seeder realized onlyprecision metering but failed to achieve precision seeding.
Given the current theoretical and experimental problems on soil covering androlling parts in the existing research of the precision seeder, soil covering and rollingparts which greatly affect the status of soil flow after seed contacting soil and thedegree of soil compaction were taken as the study object. And then the position afterseed contacting soil and the thickness of soil covering were studied thoroughly andsystematically in this paper. The eight-shaped coverer, double-disc coverer andsqueeze-type coverer were made with organic glass and a variable force seedlingsroller with pressure sensor was also designed and developed. The seed leveldisplacement and thickness influenced by the structure motion parameters of threecovers during the soil covering process were analyzed through uniform experimentaldesign method and high-speed camera system. The influence of actual sowing depth and displacement changes caused by different pressure with roller was studiedthrough orthogonal experimental design method, the related mathematical modelswere developed and the best coverer type, structure motion parameters and pressureswere optimized. The simulation analyses of the state of soil movement and seedmotion in the process of covering and rolling were done using the SPH method inLS-DYNA software. The virtual manufacturing and motion simulation of unit coverand roller of precision seeder were studied with Solidworks software and the designaccuracy and efficiency were improved.
This paper is part of the Specialized Research Fund for Doctoral Program ofHigher Institution (20040183024), the Program of Science and TechnologyDepartment of Jilin Province (200405045) and the earmarked fund for ModernAgro-industry Technology Research System(CARS-01-33), the main contents are asfollows：
1. Three different types of soil covers comprising of eight-shaped coverer,double-disc coverer and squeeze-type coverer were developed.The angle, height,width and the front and back position of the covering components can be adjusted,so that the parameters are easy to be optimized. This structure can realize trials tomeasure the position after seed contacting soil in different conditions. Thesimulation models of three types of the soil cover and roller were developed usingSolidworks software and three different soil cover were made with transparentorganic glass in order to observing the motion state of the soil flow and seedsconveniently.
2. The test of soil covering with three-type covers was accomplished on the soilbin tester based on high-speed camera technology and regression models of the seeddisplacement and the soil thickness were established under different conditionsusing the uniform experimental design method.
The regression model of the seeds’ displacement of the eight-shaped coverer inthe soil is:
The regression model shows that the primary and secondary factors affectingthe seed displacement of the eight-shaped coverer during the covering process werethe interaction of the field angle and the forward velocity of machine, the forwardvelocity of machine, the interaction of field angle and inclination angle, field angle and inclination angle in sequence.
The regression model of the soil covering thickness of the eight-shapedcoverer in the soil is:
The regression model shows that the primary and secondary factors affectingthe covering thickness of the eight-shaped coverer during the covering processwere the field angle, the interaction of field angle and inclination angle, theinteraction of covering device’s field angle and the forward velocity of machine, theinclination angle in sequence.
The regression model of the seed displacement of the double-disc soil cover inthe soil is:
The regression model shows that the primary and secondary factors affectingthe seed displacement of the double-disc coverer during the covering process werethe interaction of field angle and inclination angle, the inclination angle, the forwardvelocity of machine, the field angle, the interaction of the inclination angle and thespeed of operation in sequence.
The regression model of the soil covering thickness of the double-disc soilcover in the soil is:
The regression model shows that the primary and secondary factors affectingthe covering thickness of the double-disc coverer during the covering process insequence were the interaction of field angle and inclination angle, the interaction ofthe inclination angle and the speed of operation, the interaction of the inclinationangle and the speed of machine, the interaction of the field angle and the operatingspeed, the inclination angle, the field angle, finally, the operating speed.
The regression model of the seeds’ displacement of the extrusion soil cover inthe soil is:
The regression model shows that the primary and secondary factors affecting the seed displacement of the squeeze-type coverer during the covering process insequence were the interaction of the field angle and the operating speed, theoperating speed.
The regression model of the soil covering thickness of the extrusion soilcover in the soil is:
After the optimization of the above regression models, the optimumexperimental levels of the three types of soil cover are derived and the squeeze–typecover is defined as the optimal one. The optimal trial level is where the forwardvelocity of machine X1=4km/h, the inclination angle of the covering disc X2=30°,In this condition, the seed minimal displacement is△Y_1=0.0075m, the soilthickness△Y_2=0.0389m.
The regression model shows that the primary and secondary factors affectingthe covering thickness of the squeeze-type coverer during the covering process insequence were the field angle, the operating speed, finally, the interaction of thefield angle and the operating speed.
3、Based on the smooth particle hydrodynamics method(SPH), The dynamicssimulation for soil motion status, seed’s displacement, covering thickness and theactual sowing depth were finished during the soil covering process with the soilcoverer. The measurement of soil physical parameters and mechanical parameterswas completed. The simulation results and the test results are consistent with eachother. seed displacement error of the eight covering process is Y_1=0.002m,covering thickness error is Y_2=0.012m; seed’s displacement error of the doubleround type covering process is Y_1=0.0068m, covering thickness error is
Y_2=0.003m. These results showed that using SPH to do simulation on contactingparts of the precision seeder is feasible.
4、A variable force seedlings roller realizing that the rolling pressure fromquantitative regulation to stepless regulation was developed. The variable forceseedlings roller was developed making use of the Solidworks parametric modelingsoftware. Rolling pressure test system also were constituted using S-shaped sensor,digital display, computer and the tractor hydraulic components, which could realizethe rolling pressure from quantitative regulation to steptless regulation.
5、Experimental study of the variable force seedlings roller was conducted. Theinfluence of rolling pressure and operating speed on the actual planting depth, the Seed displacement change, the firmness of the seedbed soil, germination rate,moisture content and seedling height were systematically analyzed. The orthogonalexperiment results show that the actual sowing depth reduced while the rollingpressure increased, the other test indices increased with the increase of the rollingpressure. Among them, the firmness index of the seedbed soil and seed displacementchange index increase faster with the rolling pressure persistently adding, plantheight decreases with the rolling pressure persistently increasing, and the rest of thetest indices increase slowly with the rolling pressures persistently increasing. Theseed displacement change in the impact of the rolling pressure changes was explored.The results showed that the size of the rolling pressure on seed grain distance changehas little effect, but has a greater impact on covering thickness. The influence ofrolling pressure on all test indices is greater than the influence of the operationspeed.
6、The soil model was established using SPH softward and LS-DYNA rollingsimulation system has also been realized based on the SPH/FEM coupling algorithm.Based on the parametric modeling Solidworks software, a variable force seedlingsroller was developed and the motion simulation was carried out with the selection of1600-1800N rolling pressure and6km/h operation speed in the process. Simulationresults and the actual test results are close. The seed displacement error during therolling process is△Y_1=0.003m, the covering thickness error is△Y_2=0.0017m. It shows that the SPH method was feasible to simulate in the rolling process.
The structure parameters and motion parameters of soil coverer and roller in theprecision seeder were studied thoroughly and systematically and the SPH methodwas used to do kinematics simulation analysis in this paper. This research provides anew approach to improve the design quality of the precision seeder, and it hasimportant significance for enriching precision seeding theory
鉴于目前在精密播种机的研究中，关于覆土与镇压部件理论上和试验研究方面存在的问题，本文以对种子触土后土壤的运动状态、土壤压实程度影响较大的覆土器和镇压器为研究对象，对种子触土后位置和覆土厚度进行了深入、系统的研究。利用有机玻璃板制作了挤压式、双圆盘式、八字形覆土器，以及自行研制的装有压力传感器的可变力苗带镇压器，通过均匀设计设计方法及高速摄像系统等，分析了三种覆土器结构参数与运动参数对覆土过程中种子水平位移量与覆土厚度的影响；通过正交试验设计方法进行了镇压器的不同镇压力对实际播深、位移变化等影响的试验研究，并建立了相关数学模型，优化出了最佳覆土器种类和最佳结构参数与运动参数及最佳镇压力。利用LS—DYNA软件中SPH方法进行了覆土和镇压过程中土流与种子运动状态进行了仿真分析，应用Solidworks软件对精密播种机单体覆土器与镇压器进行了虚拟制造和运动仿真，提高了设计的准确性和效率，为进一步提高精密播种机设计质量和丰富精密播种理论进行了有益的探索。
本文是高等学校博士学科点专项科研基金（20040183024）和吉林省科技发展计划项目（200405045）、国家现代农业产业技术体系建设专项资金（CARS-01-33）的部分内容，其主要研究内容如下：
1、研制了八字形、双圆盘式和挤压式三种不同工作原理的新型覆土器，覆土部件的角度、高度、宽度、前后位置均可调节，便于参数优化，可实现不同条件下种子触土后位置变化的试验研究。基于Solidworks软件建立了三种覆土器与镇压器的仿真模型，利用透明有机玻璃板制成了三种覆土器，方便试验过程中对土流与种子运动状态观测。
2、基于高速摄像技术在土槽实验台上完成了三种覆土器覆土过程测试试验，利用均匀设计设计方法建立了不同条件下种子位移量和覆土厚度的回归模型，覆土器回归模型如下：
八字型覆土器种子位移量回归模型为：
回归模型表明：影响八字形覆土器种子位移量的主次因素依次为覆土器张角与机器速度的交互项、机器速度、张角与倾角的交互项，最后是张角与倾角。
八字形覆土器覆土厚度回归模型为：
回归模型表明：影响八字形覆土器覆厚度的主次因素依次为覆土器倾角、张角与倾角的交互项、张角与机器速度的交互项，最后是覆土器张角。
双圆盘式覆土器种子位移量回归模型为：
回归模型表明：影响双圆盘式覆土器种子位移量的主次因素依次为覆土器倾角和张角的交互项、张角、机器速度、倾角，最后是作业速和张角的交互项。
双圆盘式覆土器覆土厚度的回归模型为：
回归模型表明：影响双圆盘式覆土器覆土厚度的主次因素依次为覆土器张角与倾角的交互项、作业速度与张角的交互相、速度和倾角的交互项、张角、倾角，最后是作业速度。
挤压式覆土器种子位移量回归模型为：
回归模型表明，影响挤压式覆土器种子位移量的主次因素依次为速度与倾角的交互项、作业速度。
挤压式覆土器覆土厚度回归模型为：
回归模型表明：影响挤压式覆土器覆土厚度的主次因素依次为覆土器倾角、作业速度，最后是作业速度与倾角交互项。
经过对上述回归模型优化后，得出了三种覆土器的最优试验因素水平，并确定了最优覆土器为挤压式覆土器，最优试验因素水平为作业速度X1=4km/h，覆土圆盘倾角X_2=300，此时种子最小位移量为△Y_1=0.0075m，覆土厚度为△Y_2=0.0389m。
同时进行的高速摄像试验结果表明，覆土前种子位移量都很小，决定覆过程中种子位移变化的主要原因是种子被覆盖后随土流一起运动而引起的。八字形与双圆盘式覆土器覆土过程引起的土流运动剧烈，种子位移变化量大，同时覆土厚度也大；挤压式覆土器覆土过程对种床土壤扰动量很小，因此，种子的位移量小，覆土厚度适宜。
3、基于光滑粒子流体动力学方法（SPH），完成了覆土器覆土过程中土壤运动状态、种子位移量、覆土厚度和实际播深等动力学仿真，完成了土壤物理参数及力学参数的测定。仿真结果与试验结果基本吻合：八字形覆土器覆土过程种子位移量仿真与试验结果误差为△Y_1=0.002m,吻合程度为75.5%，覆土厚度误差为△Y_2=0.012m，吻合程度为80%；双圆盘式覆土器覆土过程种子位移量仿真与试验结果误差为△Y_1=0.0068m,吻合程度为71.8%，覆土厚度误差为△Y_2=0.019m,吻合程度为90.2%；挤压式覆土器覆土过程种子位移量仿真与试验结果误差为△Y_1=0.003m,吻合程度为76.6%,覆土厚度误差为△Y_2=0.003m吻合程度为89.9%，表明了利用SPH方法进行精密播种机触土部件仿真的可行性。
4、研制了一种可变力苗带镇压器，可实现镇压力由定量调节变为无级调节。利用Solidworks参数化建模软件建立了可变力苗带镇压器三维实体模型，制作了试验样机，利用S形传感器、数字显示器、计算机以及拖拉机液压元件构成镇压力测试系统，实现镇压力由定量调节变为无级调节。
5、进行了可变力苗带镇压器试验研究，系统分析了镇压力、作业速度对实际播深、种子位移量、种床土壤坚实度、出苗率、含水率及苗期植株高度的影响。结果表明：实际播深随镇压力加大而减少，其它试验指标均随镇压力的加大而提高，其中，种床土壤坚实度指标与种子位移变化量指标随着镇压力加大而增加更快，植株高度随镇压力继续加大而减小，其余试验指标则随镇压力继续加大而增加缓慢；探索了镇压力变化对种子位移量的影响，即镇压力大小对种子的粒距变化影响不大，但对覆土厚度有较大影响。镇压力对所有试验指标的影响均大于作业速度的影响。
6、利用SPH软件建立了土壤模型，基于SPH/FEM耦合算法的镇压系统LS-DYNA仿真实现。基于Solidworks参数化建模软件建立了可变力苗带镇压器三维实体模型，选取1600N～1800N镇压力和6km/h作业速度进行了镇压过程运动仿真，模型仿真结果与实际试验过程测试指标值接近，镇压器镇压过程种子实际位移与仿真位移误差为△Y_1=0.003m,吻合度为81.3%,实际覆土厚度与仿真过程获得覆土厚度误差为△Y_2=0.0017m，吻合度为96%。表明利用SPH方法对镇压器镇压过程进行仿真的方法是可行的。
本文针对精密播种机覆土器与镇压器两种触土部件的结构参数与运动参数进行了深入系统的研究，并通过SPH方法进行了动力学仿真分析，为提高精密播种机设计质量提供了新的研究法，对丰富精密精密播种理论具有重要意义。
The quality of precision seeding is comprehensively determined by theperformance of the five main working parts comprising of copying, trenching,metering, soil covering and rolling. The structure and performance issues of any partwill affect the overall quality of precision seeding operations. However, the researchon the above five parts were attached different importance in the past. A largenumber of literature data indicated that early research of precision seedingtechnology mainly focused on the ability to provide a uniform seed flow, whichresulted in the metering device’ quality and performance is superior to other parts inthe five major parts of precision seeding and its technical theory was also in theleading position. Until1990s, the experimental study of the other main workingparts has been paid more attention gradually, which developed the precision seedingtheory. The quality of precision seeding has also been greatly improved and theprecision seeding technology has gained rapid popularization subsequently.However, there is still lack thorough and systematic study in soil covering androlling parts. Neither fully considers the type characteristics, optimization of thestructure and motion parameters of soil covering and rolling parts, nor attaches moreimportance to the machining quality, which lead that precision seeder realized onlyprecision metering but failed to achieve precision seeding.
Given the current theoretical and experimental problems on soil covering androlling parts in the existing research of the precision seeder, soil covering and rollingparts which greatly affect the status of soil flow after seed contacting soil and thedegree of soil compaction were taken as the study object. And then the position afterseed contacting soil and the thickness of soil covering were studied thoroughly andsystematically in this paper. The eight-shaped coverer, double-disc coverer andsqueeze-type coverer were made with organic glass and a variable force seedlingsroller with pressure sensor was also designed and developed. The seed leveldisplacement and thickness influenced by the structure motion parameters of threecovers during the soil covering process were analyzed through uniform experimentaldesign method and high-speed camera system. The influence of actual sowing depth and displacement changes caused by different pressure with roller was studiedthrough orthogonal experimental design method, the related mathematical modelswere developed and the best coverer type, structure motion parameters and pressureswere optimized. The simulation analyses of the state of soil movement and seedmotion in the process of covering and rolling were done using the SPH method inLS-DYNA software. The virtual manufacturing and motion simulation of unit coverand roller of precision seeder were studied with Solidworks software and the designaccuracy and efficiency were improved.
This paper is part of the Specialized Research Fund for Doctoral Program ofHigher Institution (20040183024), the Program of Science and TechnologyDepartment of Jilin Province (200405045) and the earmarked fund for ModernAgro-industry Technology Research System(CARS-01-33), the main contents are asfollows：
1. Three different types of soil covers comprising of eight-shaped coverer,double-disc coverer and squeeze-type coverer were developed.The angle, height,width and the front and back position of the covering components can be adjusted,so that the parameters are easy to be optimized. This structure can realize trials tomeasure the position after seed contacting soil in different conditions. Thesimulation models of three types of the soil cover and roller were developed usingSolidworks software and three different soil cover were made with transparentorganic glass in order to observing the motion state of the soil flow and seedsconveniently.
2. The test of soil covering with three-type covers was accomplished on the soilbin tester based on high-speed camera technology and regression models of the seeddisplacement and the soil thickness were established under different conditionsusing the uniform experimental design method.
The regression model of the seeds’ displacement of the eight-shaped coverer inthe soil is:
The regression model shows that the primary and secondary factors affectingthe seed displacement of the eight-shaped coverer during the covering process werethe interaction of the field angle and the forward velocity of machine, the forwardvelocity of machine, the interaction of field angle and inclination angle, field angle and inclination angle in sequence.
The regression model of the soil covering thickness of the eight-shapedcoverer in the soil is:
The regression model shows that the primary and secondary factors affectingthe covering thickness of the eight-shaped coverer during the covering processwere the field angle, the interaction of field angle and inclination angle, theinteraction of covering device’s field angle and the forward velocity of machine, theinclination angle in sequence.
The regression model of the seed displacement of the double-disc soil cover inthe soil is:
The regression model shows that the primary and secondary factors affectingthe seed displacement of the double-disc coverer during the covering process werethe interaction of field angle and inclination angle, the inclination angle, the forwardvelocity of machine, the field angle, the interaction of the inclination angle and thespeed of operation in sequence.
The regression model of the soil covering thickness of the double-disc soilcover in the soil is:
The regression model shows that the primary and secondary factors affectingthe covering thickness of the double-disc coverer during the covering process insequence were the interaction of field angle and inclination angle, the interaction ofthe inclination angle and the speed of operation, the interaction of the inclinationangle and the speed of machine, the interaction of the field angle and the operatingspeed, the inclination angle, the field angle, finally, the operating speed.
The regression model of the seeds’ displacement of the extrusion soil cover inthe soil is:
The regression model shows that the primary and secondary factors affecting the seed displacement of the squeeze-type coverer during the covering process insequence were the interaction of the field angle and the operating speed, theoperating speed.
The regression model of the soil covering thickness of the extrusion soilcover in the soil is:
After the optimization of the above regression models, the optimumexperimental levels of the three types of soil cover are derived and the squeeze–typecover is defined as the optimal one. The optimal trial level is where the forwardvelocity of machine X1=4km/h, the inclination angle of the covering disc X2=30°,In this condition, the seed minimal displacement is△Y_1=0.0075m, the soilthickness△Y_2=0.0389m.
The regression model shows that the primary and secondary factors affectingthe covering thickness of the squeeze-type coverer during the covering process insequence were the field angle, the operating speed, finally, the interaction of thefield angle and the operating speed.
3、Based on the smooth particle hydrodynamics method(SPH), The dynamicssimulation for soil motion status, seed’s displacement, covering thickness and theactual sowing depth were finished during the soil covering process with the soilcoverer. The measurement of soil physical parameters and mechanical parameterswas completed. The simulation results and the test results are consistent with eachother. seed displacement error of the eight covering process is Y_1=0.002m,covering thickness error is Y_2=0.012m; seed’s displacement error of the doubleround type covering process is Y_1=0.0068m, covering thickness error is
Y_2=0.003m. These results showed that using SPH to do simulation on contactingparts of the precision seeder is feasible.
4、A variable force seedlings roller realizing that the rolling pressure fromquantitative regulation to stepless regulation was developed. The variable forceseedlings roller was developed making use of the Solidworks parametric modelingsoftware. Rolling pressure test system also were constituted using S-shaped sensor,digital display, computer and the tractor hydraulic components, which could realizethe rolling pressure from quantitative regulation to steptless regulation.
5、Experimental study of the variable force seedlings roller was conducted. Theinfluence of rolling pressure and operating speed on the actual planting depth, the Seed displacement change, the firmness of the seedbed soil, germination rate,moisture content and seedling height were systematically analyzed. The orthogonalexperiment results show that the actual sowing depth reduced while the rollingpressure increased, the other test indices increased with the increase of the rollingpressure. Among them, the firmness index of the seedbed soil and seed displacementchange index increase faster with the rolling pressure persistently adding, plantheight decreases with the rolling pressure persistently increasing, and the rest of thetest indices increase slowly with the rolling pressures persistently increasing. Theseed displacement change in the impact of the rolling pressure changes was explored.The results showed that the size of the rolling pressure on seed grain distance changehas little effect, but has a greater impact on covering thickness. The influence ofrolling pressure on all test indices is greater than the influence of the operationspeed.
6、The soil model was established using SPH softward and LS-DYNA rollingsimulation system has also been realized based on the SPH/FEM coupling algorithm.Based on the parametric modeling Solidworks software, a variable force seedlingsroller was developed and the motion simulation was carried out with the selection of1600-1800N rolling pressure and6km/h operation speed in the process. Simulationresults and the actual test results are close. The seed displacement error during therolling process is△Y_1=0.003m, the covering thickness error is△Y_2=0.0017m. It shows that the SPH method was feasible to simulate in the rolling process.
The structure parameters and motion parameters of soil coverer and roller in theprecision seeder were studied thoroughly and systematically and the SPH methodwas used to do kinematics simulation analysis in this paper. This research provides anew approach to improve the design quality of the precision seeder, and it hasimportant significance for enriching precision seeding theory
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