| Core is one of the most important food and fodder crop in China,which plays an important role in ensuring food security.Precision sowing is an effective technology to improve maize yield.At present,the mechanical metering device is mainly used in precision seeding in our country,which has the advantages of easy manufacture,simple structure and low cost.However,due to the influence of seed selection or filling method,the seeding leakage rate is relatively high.Aiming at the problems of high leakage rate and uneven plant spacing distribution of the existing maize metering device in the process of mechanical operation,in this paper,manufacturing and performance test of the metering device was carried out based on the previous research group.For the problems in the test,the structure of the metering device was improved and optimized.Finally the second generation metering device was developed and bench test research was carried out.The main work and conclusions of the dissertation are as follows:(1)Manufacturing and working performance test of seed metering device.The results showed that when the rotational speed of the metering wheel was lower than 22.7r/min,the grain spacing eligibility index met the requirement that the mechanical metering device performance index was more than 75%.When the rotational speed of the metering wheel was lower than 16.3r/min,the compensation rate can reach more than 90%.The compensation effect was better and the seed damage rate was low.During the test,it was found that the seeder still had some problems,such as difficulty in installation and commissioning,instability of linkage device and relatively high rate of seeding leakage.(2)The discrete element simulation analysis of seed meter working process.The simulation experiment was carried out by means of discrete element simulation software.Under the rotational speed of the metering wheel of 13.1r/min,the whole movement process of particles was analyzed,and the motion trajectory,velocity variation and force diagram of the single particle which was labeled and tracked were obtained.The results showed that there were some problems in the seed metering device,such as the large volume of the shell,the decrease of filling rate and the unstable plant spacing caused by the early seed leaving the nest.The force analysis of the probe seeding process was carried out.The results show that the resistance of the seed through the probe frame is related to the spring compression force.(3)Improvement design of metering device.The structure of seed metering device was improved and designed,including lock pawl,seed searching frame and rocker arm in linkage device,brush wheel and intermediate gear in transmission device,and other shaft parts.Auxiliaries and sequential teeth were added in the design.The parameters of socket hole were optimized,and the hemispherical socket hole with diameter of 11 mm,12 mm,13 mm,14 mm and 15 mm were determined.Finally,the improved seed metering device was virtual assembled and manufactured.(4)Performance test of seed metering device.The results of bench test on the improved metering device showed that when the speed of metering wheel was 16.3r/min,the length of socket was 13 mm,and the qualified index of grain spacing was 96.08%,the metering test index was the best;when the speed of metering wheel was lower than 16.3r/min,the performance index of double-row hole arrangement was better than that of single-row arrangement.Compared with the speed of metering wheel of 16.3r/min,the grain spacing eligibility index increased by 8.9% and the missing sowing index decreased by 35%. |
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