Theory And Experimental Research Of Sowing Depth Control For Precision Seeder Unit

Precision seeding technology has been successfully applied to a variety of crops， and itis one of the important measures to increase the agricultural production and income， andreduce the cost of grain production. Precision seeding technology includs accurate seedingrate， precise rows space and sowing depth， so as to ensure the reasonable distribution ofseed in the field，and create the best conditions for crop growth and development. Precisionseeding process is make up of profiling，ditching，applying fertilizer，sow，cover earth，rolling and so on， the many kinds of working parts cooperated to complete a complexprocess， and its demand of field index is accurate， any link may affect the final accuracy.At present most scholars’ study focused on precision seeding theory and development ofvarious seeding apparatus， and many kinds of precision seeding apparatus had beendeveloped for example gas suction，gas blowing，scoop types and so on，and the accuratesowing amount had been realized. But sowing depth and row spaces are formed byprofiling， furrowing， covering， suppressing， and closely related to the soil conditionof seed groove. All parts may influence the seeds final distribution state in the soil.Consistency of sowing depth and quality of covering seeds had important effects on theseeds emergence and the crop yield， so precision seeder’s consistency of sowing depth andquality of covering seeds decided sowing quality is ok or not. However， lacking ofthorough and systematic research of influence to sowing depth accurate profile and ditchdevice， the actual sowing depth had been less than the best condition.This paper researched precision seeder profiling mechanism that influences sowing depthcontrol， by using mechanisms and dynamics， soil rheology， and by testing therelationship of soil subsidence quantity and time， then defined the dry farmland soilrheological model and rheological parameters， established the regression model about soilsubsidence quantity and related parameters. Introduced the soil rheological model intodynamics analysis about parallel four-bar type precision seeding unit， established amathematical model of ditching depth changes about parallel four-bar profiling mechanism.Used Matlab software to simulate ditch depth， analyzed the parameter that could effectditch depth and its variation rule， found out the effecting factors on the stability of ditchdepth.By using parametric design function of Pro/E software to establish3D parametricmodel database of precision seeder，and used ADAMS software to optimize structureparameters design and simulate motion of parallel four-bar precision seeding monomerprofiling mechanism what had been built，analyzed ditch depth of profiling mechanism andtested the stability of ditch depth indoor，the results of simulation and experiment were verysimilar. At last developed a kind of precision seeding unit that combined parallel four-bar profiling mechanism with electric-hydraulic automatic controlled profiling system in orderto satisfy accuracy of sowing depth control in large-sized precision seeder， designed theprofiling sensing device， profiling controller， hydraulic system，etc. Simulated thehydraulic system model which had been established by using Simulink software， andverified the accuracy of model through the test. Field test showed that， electronic-hydrauliccontroled profiling form was obviously superior to mechanical profiling in profilingaccuracy，it realized accurately sowing depth control， provided technical reference toimprove the automation degree of the large precision seeder.This paper is parts of university Specialized Research Fund for the Doctoral Program ofHigher Education20040183024)，Science and Technology Development Program of JiLinProvince (200405045)，Construction of National Modern Agriculture Industrial TechnologySystem Specialized Fund (CARS-01-33)， its main content and research conclusions asfollows:（1）By the test of uniaxial compression to soil， observed the deformation curve aftersoil being beard related to time variation， selected four-element Burgers model to describerheological characteristics of soil， and obtained the equation for soil deformation related totime variation:by the equation，it was known that soil subsidence deformation is mainly composed ofthree parts that are instantaneous subsidence， time-delay subsidence and stable creep. Thequation also suggested that subsidence deformation of loose soil related to time， and it wasnonlinear. Based on this theory，got the soil rheological curve under the condition that townpressure was400N，600N，800N， and soil moisture content was16%，18%，20%，by the way of experiment. Got soil rheological parameter at different experiment conditionsby the way of the numerical simulation， and determined soil rheological model under thecorresponding conditions.（2）In order to obtain the relationship between soil subsidence quantity and influencefactors， selected the moisture content， suppression strength and operation speed asinfluence factors， obtained the regression equation as follows of soil subsidence quantityand the related factors by optimized the test scheme of response surface design：It can be concluded from the regression model that the relationship between soil subsidence quantity and suppression strength， moisture content， operation speed wasnonlinear. The main influence factor to subsidence quantity was suppression strength，followed by soil moisture content. Though only a little effect， the operation speed wasnegatively correlated to subsidence quantity. The influence relation between correlationfactors and soil cave in quantity could be analyzed more intuitively by this regressionmodel.（3）Researched parallel four-bar profiling precision seeder monomer as the object，introduced soil rheological parameter，established mathematical model of precision seedingmonomer’s sowing depth:This model showed that profiling process of sowing monomer was linear single freedegree damping vibration system， the system’s stability was related to geometriccharacteristics of field surface，structure parameters of sowing monomer and mechanicsproperties of soil. K2and η2are spring stiffness coefficient and damping coefficient， A isdeformation coefficient related to instantaneous subsidence quantity and time-delaysubsidence quantity， it could be calculated by using of the soil subsidence quantityregression model. One better combined parameter obtained after analyzed the influencefactors of precision seeding monomer profiling， ditching stability， and simulated ditchingdepth by using Matlab software.（4）By the function of Pro/E software parametric design，constructed the3D parametricmodel base of precision seeder parts， established a different forms of seeder monomerentity model in3D. Ditching depth as a target， Based on the structure parametersoptimization design and movement simulation of parallel four-bar precision seedingmonomer profiling institutions， obtained the most optimal parameter value by using theADAMS software: If the length was450mm for parallel four-bar， and the distance was300mm from preposed profiling wheel to opener， ditching stability could satisfy the designrequirement.（5）The test results and the profiling results were similar after the research of ditchingdepth stability indoor. Verified correctness of dynamic model what the seeding monomerhad been established and reliability of the simulation analysis method.Analyzed ditch depth of profiling mechanism and tested the stability of ditch depthindoor，the variation trend of the simulation and experiment results were very similar，andthe largest error was less than23%，verified the stability of mathematics model for ditchdepth was correct and the simulation analysis method was reliable in this paper.（6）Developed the precision seeding monomer that combined parallel four-bar mechanism and electric-hydraulic controlled profiling system. Designed the requiredprofiling device， sensing device， profiling controller， hydraulic system， established thesimulation model of hydraulic system. Simulated the movement of the hydraulic systemby using Simulink software. According to the test results， the simulation value andexperimental results was similar， the maximum error was16.4%，which met the designrequirements and verified the correctness of the model. Comparative test was done betweenthe two different profiling sowing monomer， electric hydraulic automatic and mechanicalprofiling seeding monomer in the field，and the results showed that electro-hydraulicautomatic profiling form is obviously superior to the mechanical profiling form at profilingaccuracy， and satisfied accuracy control of sowing depth， improved automation degree ofthe large precision seeder.The research conclusions in this paper about theory， experiment and computersimulation provided a new train of method for development precision seeder and formodeling and profiling design agricultural machinery system. Its significance was importantto enrich precision seeding theory and develop precision seeding technology.