| The fact that rural labor transfers to the city very fast leads to the shortage of rural labor and increasing agricultural production cost.The seeds are hill-dropped in the exact position on the paddy surface uniformly by using the precision rice hill-drop drilling technology to save seeds and increase yield.The precision rice hill-drop drilling technology also can save time,labor and energy without the processes of seedling raising,transferring and transplanting.Consequently,the precision rice hill-drop drilling technology is a light and simplified rice cultivation technique pattern and also a developing tend of rice direct seeding.It should meet the rice direct seeding agronomic requirements which are furrowing and ridging synchronously,with adjustable sowing rate and hill spacing,optional row spacing,profiling seeding mode and stubble burying before seeding.The precision rice hill-drop drilling machine developed in South China Agricultural University had some defects to be studied and optimized,such as limited adjusting range of sowing rate,easily damaged main bar,incomplete profiling system and incompatible hill spacing etc.,and therefore according to the actual production situation,the theoretical research and optimization of rice precision seeder were carried out.Main research contents are as follows:The physical characteristics of rice varieties in the main rice producing areas in China were studied.Based on the model of bulk solid mechanics and natural repose angle of the tested rice seeds,the seed-filling initial angle and filling process of the metering device was researched by using theoretical calculation and CAD simulation.According to the experimental results,seed-filling initial angle was confirmed as-20°.A combined hole-type metering device which has small and big type holes alternately distributed on the same roll was studied and designed.The main parameters of the hole are determined as well.The metering device has a wider adjusting range of sowing rate(3~6and 7~10,two levels),and it was very easy to exchange.Consequently,it has good adaptability of seeding both conventional and hybrid rice seeds,and it could meet requirements of rice production.The key parameters of the seeds flow adjusting mechanism were calculated and verified through experiments.The results showed that the seeds flow adjusting mechanism can realize the micro adjustment of 1 seeds at a higher speed.Furthermore,the optimal design of the seed protection mechanism was carried out.The experiment results showed that the reliability of the flexible seed protecting device with copper axle sleeve and needle bearing is much better,and the seeds breakage can be reduced by more than 79.2%.Furrowing device and profiling system is the key to ensure furrowing and ridging effect of the precision rice hill-drop drilling machine.According to the width of seeds hill and rice cultivation agronomic requirements,the main parameters of the seed furrow opener were determined to be 50 mm×35 mm×30 mm(upper width×lower width×height);Due to the soil mechanical properties and the mass distribution of the seeding machine,the main parameters of the water furrow opener are 80 mm×50mm×60 mm(upper width×lower width×height);And both were shaped as boat.The suitable soil moisture content to furrowing and ridging was determined to be 48%~.55%through theoretical analysis and field test.The parameters of the horizontal profiling mechanism and the key components of the height profiling mechanism were optimized.The interactions between profiling mechanism and soil were studied by theoretical analysis.The results showed that the horizontal and height profiling mechanism could make the seeded field surface relatively flatter after sowing,and it was conducive to seedling emergence.The seedling emergence rates of the rice varieties Xiushui134 and Peizataifeng,which were seeded by using the precision rice hill-drop machine with horizontal profiling mechanism,were 7.8%and 8.7%higher than that without horizontal profiling mechanism,respectively.The stubble-burying seeding method was studied.The angle of the slide board was confirmed as 4°according to the experiment result,while the efficiency of stubble burying was 91.6%and the furrowing and ridging effect under 4°was relatively better than that under other degrees.The mass center distribution of 25cm row-spacing rice precision hill-drop drilling machine with Yanmar VP6D and VP6G was studied.In working conditions,the mass center distribution ratio of the above two models of machine were 66.1%and 68.2%,respectively,which met the requirement of the best mass distribution of the paddy machine.The test results from YNC R&D Center of Yanmar(China)Co.,Ltd.showed that the transverse and longitudinal stability of seeder were qualified,and therefore the mass center distribution was designed reasonably.According to the results of the reliability test,the structure of bearing seat connecting frame and the main bar for seed metering device were optimized,and the strength requirement was achieved.In this paper,verification tests were conducted on the main technical indices of the seeding machine and its reliability.Results showed that,the qualified rate of the seeds number per hill reached 95%and the cavity rate was 0,the pure work efficiency was 0.67hm~2/h;furthermore,the variation coefficient of the consistency of seeding quantity per row and the stability of total seeding quantity were 3.8%and 1.5%,respectively;after seeding the height difference of the field surface was about 2.0 cm;more important,the mean time to first fault(MTTFF)was 30.4 hm~2/m,and the validity reached up to 98.2%.Therefore,on the basis of these results which all meet the national standard and the requirements of the combination of agricultural machinery and agronomy.The performance of the optimized precision rice hill-drop drilling machine is reliable and has exciting application foreground.The production test of precision rice hill-drop drilling machine was carried out in Milan farm,Italy and Songjiang,Shanghai.The results showed that the yield of precision rice hill-drop drilling machine was3.5%and 22.5%higher than Italian commonly used drilling machine and spreader,respectively,and 4%and 25%higher than mechanical transplanting and manual spreading,respectively.Analyzing the application saturation of precision rice hill-drop drilling machine in China in recent years,it has good adaptability.The rice distributed in the field uniformly that resulted in good ventilation and light transmission.The plants have stronger tillering potential and more effective panicle number,leading to stable and high yield.2BDXS-10precision rice hill-drop drilling machine has good adaptability and good yield potential in direct seeding area.In conclusion,the studied and optimized precision rice hill-drop drilling machine can meet the agronomic requirements of rice precision hill-drop drilling,and its performance is highly reliable,adaptable and efficient,and therefore it can achieve having good yield potential and wide application prospect. |
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