| Rapeseed is the main oil crop in China and its planting area and total production are both first in the world.In order to improve the mechanization seeding level of rapeseed in the middle and lower reaches of the Yangtze river,a no-tillage direct seeder for the rapeseed was developed based on the current situation of rapeseed planting and agronomic requirements in this area.The seeder could realize the stubble pressing,active ditching,soil surface covering,precise sowing and fertilization functions.The basic structure,working process and technological route of the seeder were determined.Based on some typical technologies and methods like the kinematics theory,discrete element simulation and response surface design,the influence of structural and operational parameters of key soil-contact components such as active furrow cutters and soil separating plates on their performance was studied.To solve the deficiency of measuring accuracy and efficiency of traditional field surface planeness measuring device for rapeseed direct seeder,the accurate quantification of rapeseed field surface planeness characteristics was realized based on laser radar scanning technology and regional surface elevation data acquisition and processing method in this paper.Main studies include:(1)The overall design scheme of no-till seeder was determined based on the mechanical and physical properties of rice-rapeseed rotation soil and rice straw.An active rotary ditching device based on spiral motion was proposed.It combined the active ditching function with the soil throwing and covering functions by the soil separating plate,achieving the spiral rotation ditching and evenly covering of soil surface.The technical route for the rapeseed no-till seeding seed bed was obtained.The core parts of the seeder mainly included active ditching cutter,soil separating plate,stubble limit roller,centrifugal planter with electric control system,etc.The operation sequence and relative position relation of each soil-contact component were clarified,and the main technical parameters of no-tillage direct seeder were determined:The operating width was 2000 mm,the ditching depth was 160～200mm,the ditching width was 300～350 mm,and the maximum operating speed was 6 km/h.(2)The structure design and parameter analysis of the key components of the active ditching no-tillage direct seeder for rapeseed were carried out.Including:(1)A kind of active rotating ditching device composed of front and rear cutters was proposed.Each cutter included an inner and outer layer of blades.The front and rear cutters cut in reverse sequence,and the inside and outside blades of each cutters were evenly distributed.The active rotating ditching device moved in a spiral way,breaking through the limitation of the operating speed of the traditional trochoid rotary tillage.To keep the soil cutting amount of front and rear cutters the same,the rotating radius of the inner and outer blades of the front and rear cutter was determined.A kind of ditching blade that was good for root crushing and easy for produced was designed.(2)Based on the analysis of the characteristics of the front and rear cutters’concentrated throwing angle area,the front soil separating plate with adjustable angle and fixed area,and the rear soil flow diversion curved plate with adjustable angle were designed.According to the requirements of the width of the furrow on both sides,the size parameters of the soil separating plates were determined.(3)The front wide stubble limit roller with vertical load formed by tractor traction and seeder gravity was designed.The factors influencing the amount of subsidence in the process were analyzed.The diameter and width of the roller were 273 mm and 2000mm,respectively.(4)An electronic centrifugal seed metering system was developed to realize the closed loop control function of the seed metering variable based on the feedback regulation of the operating speed of the tractor.The structure of transmission system was simplified and the stability of seeding performance was improved.(3)The migration process of soil particles under the action of ditching blade and soil separating plates was analyzed.Including:(1)The kinematics model of soil particles was established according to the force and motion status of soil particles during cutting and throwing process.Based on the analysis of the structure and motion parameters of the cutter,the motion differential equation of soil particles on the tangent surface of the blade in the moving and fixed coordinate system was established.In the fixed coordinate system,the influence factors of soil particle throwing motion were analyzed.The throwing velocity and angle were not only related to the structural parameters like rotary diameter,bending angle and geometric dimension of the cutting blade,but also related to operating parameters such as cutter speed,forward velocity of the seeder,and soil friction coefficient.(2)By solving the nonlinear differential equations,the range of typical throwing velocity of the front and rear cutters was 8.6～13.7 m/s and 9.1～14.4m/s,respectively.The transverse throwing angle range was 35.1～69.3°and 56.3～81.7°,respectively.(3)Based on the analysis of the motion law of soil particles,the motion modeling and analysis of the collision process between soil particles and soil separating plates were carried out.The constraint condition of collision between soil particles and soil separating plates was established based on the results of soil particles throwing velocity and angle.The spatial coordinate expression of soil particle collision time was obtained.The trajectory equation of soil particles and soil separating plates after collision was established based on the theory of elastic-plastic particle collision theory.The constraint mechanism and influence condition of the width of transversal throwing soil were clarified,which provided theoretical support for accurate adjustment of the transversal throwing distance of soil.(4)EDEM simulation software was used to carry out the optimal combination of key structural parameters of ditching blades and the simulation experiments of structure and operational parameters of soil separating plates.The results of the simulation showed:(1)The minimum power consumption was 12.61k W when the bending angle and bending radius of the blade were 20°and 60 mm,respectively,under the operating conditions of the ditching depth of 180mm,cutter speed of 800r/min and forward velocity of 1m/s.(2)According to the soil surface difference formed by the round-trip operation sequence of the seeder,the order of significant influence on the soil surface planeness formed by the front soil separating plate during the round-trip operation was the adjustment angle>the installation height>the inclined installation distance.The optimal soil surface planeness was 7.61 mm when the installation height was 383.3 mm,the adjustment angle was 6.5°,and the inclined installation distance was 146.4 mm;and the order of significant influence on the soil surface planeness formed by the rear soil separating plate during the round-trip operation was the adjustment angle>the installation height>the transverse installation distance.The optimal soil surface planeness was 8.62mm when the installation height was 325.0mm,the adjustment angle was 3.5°,and the transverse installation distance was 96.6mm.The reliability of simulation results was verified by field experiments.(5)Field experiments were carried out on the performance of rapeseed active ditching no-tillage direct seeder.The soil surface of rice-rapeseed rotation area under different working conditions was selected,and the performance test of the seeder was carried out within the designed operating parameters,focusing on the indexes such as stubble compression performance,ditching stability,soil surface planeness,and soil breaking rate.In order to realize the precise quantification of soil surface,a set of surface micro geomorphology measurement device based on lidar scanning technology was designed to overcome the shortcomings of the measurement accuracy and efficiency of the traditional measuring device.The typical resolution of the device was 3.8～10 mm in the scanning direction of the lidar,and the vertical scanning direction could be set arbitrarily in the range of millimeter accuracy.The typical coverage area of the measured area was 6.8 m~2,and the fastest single measurement time was less than 2.5 min.The results showed that:(1)The average furrow depth and width formed by active rotation of the ditching cutter were 157.4～186.7mm and314.7～336.8mm,respectively.The stability of the furrow depth and width under the same operation conditions were both higher than 90%,which meet the agronomic requirements.(2)High moisture content(more than 35%)was beneficial to improve the performance of crushing and burying stubble.However,the stability of furrow depth,soil planeness fragmentation would be worse.The improvement of forward velocity of the seeder would reduce the rate of soil breaking,stubble effect and stability of ditching depth.The increase of rotating speed of the cutter was beneficial to increase the rate of soil breaking and the planeness of soil surface.(3)The orthogonal experiment results showed that the effects of ditching depth,forward velocity and cutter speed on power consumption were very significant.The ditching depth had a very significant effect on the soil surface planeness.The forward velocity and cutter speed had significant influence on the soil surface planeness.The optimal working parameters of the seeder were as follows:the ditching depth was 180 mm,the forward velocity was 4.5 km/h,the cutter speed was 1080 r/min,the power consumption was 17.21 k W,the soil surface planeness was 13.61 mm,the soil breaking rate was 95.66%,the furrow depth and width stability were 93.48%and95.19%,respectively,which meet the requirements of agronomic requirements.(6)The quality analysis and evaluation method of the soil surface for rapeseed direct seeder were studied.Based on the design of surface micro geomorphology measuring device,the surface elevation data acquisition with the resolution of less than 10 mm was realized.Through analyzing the soil surface characteristics of rapeseed direct seeding bed,the pretreatment method of collected data was determined.The influence of soil surface inclination and slope characteristics on the roughness calculation results was reduced.Statistical results of roughness of section data at different sampling intervals and different angles showed that:In a fixed size area,16 and 64 times of equal-distance sampling were needed to make the measurement result stable.The mean root-mean-square(RMS)height and mean RMS height error at 170mm sampling interval were both higher than the calculated results at 5mm sampling interval.In the directions of 0°,45°and 90°in the vertical direction of forward velocity,the maximum difference in RMS height and the maximum difference in correlation length of the surface section elevation data were 7.69mm and25.14mm,respectively.It showed that the planeness of seed bed with structural characteristics such as seed furrow was anisotropic.The statistical results of local roughness quantization with sliding sampling windows of different sizes showed that:the standard deviation of the RMS height could be stabilized within 0.27 mm when the window width was 0.5 times the working width and the window length was not less than 1.2 m.The influence of local tilt on the roughness calculation results could be eliminated by detrend processing for each sampling window separately.The results could provide a reference for measuring and quantifying the soil surface roughness of rapeseed during mechanical direct seeding. |
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