The negative pressure of the rice air-suction seed metering device has a significant impact on the accuracy, efficiency, uniformity, low damage, and protection of sowing. However, there is a lack of convincing research on predicting the negative pressure. A fast, efficient, and concise method for predicting the negative pressure needs to be urgently studied. To address this issue, a negative pressure prediction model was proposed. Firstly, the most essential equation of the negative pressure prediction model was derived by analysis of the air-suction principle. Secondly, the rice seed gravity G of the equation was fitted to be a function by calculus and weighted average. Afterwards, the air-suction force Fa of the equation was fitted to be a function by the CFD-DEM simulation experiment. To obtain a relatively simple and accurate fitting function, the linear fitting function was chosen to represent the relationship between the air-suction force and the negative pressure. Then, the impact levels of negative pressure and rotation speed are determined to be 400-800 Pa and 30-60 r.min(-1,) respectively(.) The equivalent coefficient ,u of the equation was calculated to be 2.73 by orthogonal experiment and parameter target optimisation. Finally, the applicability of the pressure prediction model was verified by the verification experiment. The result shows that the prediction model can effectively predict the negative pressures corresponding to various rice seeds. This study provides a theoretical foundation, technical accumulation, and scientific guidance for the subsequent optimisation design of the rice air-suction seed-metering device.

The double-hole rice vacuum seed meter is critical equipment for the planting precision of rice direct seeding. The effects of shaped holes and seed disturbance on the precision of rice bunch planting were investigated to improve the precision of bunch planting with the double-hole rice vacuum seed meter. A test bench with the rice vacuum seed meter was set up to analyze the trends in the quality of feed index, miss index, and multiple index of seed meters with different shaped holes at different speeds and vacuum pressures. Based on the optimal hole structure, different seed disturbance structures were designed to investigate the influence of the seed disturbance structure on the precision of bunch planting. A multiple linear regression model was established for the relationship between the disturbance structure, vacuum pressure, rotational speed, and the precision of bunch planting. Discrete element numerical simulation experiments were carried out to analyze the effect of disturbance structures on seeds. The planting precision of the seed meter with the shaped hole was significantly higher than that of the seed meter without the shaped hole while the shaped hole B was the optimum structure. Disturbance structure affects the quality of feed index, multiple index rate, and miss index. The planting precision of the seed disturbance structure II was better than the other structures. At a speed of 60 rpm and vacuum pressures of 2.0 kPa, 2.4 kPa, and 2.8 kPa, the qualities of feed index of seed disturbance structure II were 90%, 91.11%, and 89.17%, respectively, and the miss indexes were 2.96%, 1.94%, and 1.57%, respectively. At high rotational speeds, the precision of rice bunch planting with the seed disturbance structure is better than that without the seed disturbance structure. In the simulation test, the seed velocity and total force magnitude of the meter without disturbance structures were less than those with the disturbed structure. Simulation experiments showed that the seed disturbance structure breaks up the stacked state of seeds. Research has shown that the shaped hole holds the seed in a stable suction posture, which helps to increase the seed-filling rate. Seed disturbance improves seed mobility, thereby enhancing the precision of bunch planting.

In order to achieve uniform and stable seed supply over a large sowing volume range of seed supplies in an airassisted centralized metering system for rice and wheat, the study designed a seed supply unit with an equalwidth inclined inlet based on the Venturi principle. The parameters of the seed feeding device were determined through theoretical calculation, and the DEM-CFD gas-solid coupling method was used to simulate and analyze the migration and motion characteristics of Japonica rice seed particles in the seed supply device with the average seed supply rate and seed flow rate as the experimental objectives. The following experimental factors were first optimized to show a good transport performance of seed feeding device for both indica rice and wheat seeds: the outlet height of the mixing section (36.19 mm), the angle of the inclined seed feeding section (53.41 degrees), the height of the inclined seed feeding section (50 mm), the average velocity of the seed outlet (18.67 m/s), and the average mass flow rate of the seeds (682.20 g/s). The feasibility of the simulation model was then verified through bench tests, and the coefficient of variation for displacement stability and consistency of the three seeds were all below 1.5 % and 7.0 %, respectively. The relative error between the actual seed supply rate and the theoretical seed supply rate was all below 1.5 %. This study provides a reference for analyzing the seed motion characteristics inside the seed feeding device and optimizing the structural parameters.

Pneumatic precision metering device has been mostly used for single crops in recent years. However, there are many types of vegetables with large differences in seed size. It is still lacking the pneumatic precision metering device suitable for the vegetable seeds, such as flowering Chinese cabbage, radish, and hot pepper. In this study, an air-suction wheel pneumatic precision metering device was developed for the vegetables using the seed stirring strip and seed filling. The key structural parameters of the precision metering device were determined, where the diameter of the seed-suction hole was 1.0 mm, and the number of seed-suction holes was 20. The structure of the seed stirring strip was designed with a rectangular strip of length 6 mm and width 2 mm. The direction of the long axis was also tangential to the seed-suction hole. The force of the seeds was analyzed on the seed-stirring strip during the seed-filling stage. The range of the parameters was determined in the seed-stirring strip structure. A seed cleaning device was also designed with the staggered and adjustable seed cleaning distances on both sides. Among them, the force on the seeds was analyzed in the seed-cleaning stage, in order to design the structure of the seed-cleaning finger for the gradual approach of the seed-suction hole. The test objects were selected as the seeds of Sijiu No.19 flowering Chinese cabbage, short leaf No.13 radish, and Dunjiao Chuanqi hot pepper. The preference test was carried out, where the qualified, multiple and missing rates were used as test indexes, and the inclination angle and the thickness of the seed stirring strip were used as test factors. The test results showed that there was a variation in the inclination angle and the thickness of the seed stirring strip on the seed filling performance under the different seeds. The qualified rate of each structural parameter was taken as the average value. The better parameter values were determined as the inclination angle of the seed stirring strip was 30°. The thickness of the seed stirring strip was a kind of seed stirring strip with a slope, where the thickness at the thinnest and thickest points were 0.5 and 1.0 mm, respectively. A three-factor and three-level orthogonal test was carried out with the seeding rotation speed, working negative pressure, and seed cleaning distance as the test factors.The regression analysis was also performed to obtain a better combination of working parameters. In flowering Chinese cabbage seeds, the qualified rate, multiple rate, and missing rate were 99.20%, 0.67%, and 0.13%, respectively, when the working negative pressure was 0.92 k Pa, the seeding rotation speed was 13.3 r/min, and the seed cleaning distance was 0.70 mm. In radish seeds, the qualified rate, multiple rate and missing rate were 97.34%, 2.13%, and 0.53%, respectively,when the working negative pressure was 4.47 kPa, the seeding rotation speed was 25.5 r/min, and the seed cleaning distance was 1.20 mm. In hot pepper seeds, the qualified rate, multiple rate and missing rate were 88.27%, 9.06%, and 2.67%,respectively, when the working negative pressure was 1.49 k Pa, the seeding rotation speed was 16.9 r/min, and the seed cleaning distance was 0.69 mm. The new device fully met the agronomic requirements of flowering Chinese cabbage, radish,and hot pepper. The finding can provide a strong reference to design the air-suction wheel precision metering device for vegetables.

In order to investigate the flow characteristics and distribution law of airflow in multi-branch pipe of pneumatic rice precision direct seeder and obtain the mathematical model between airflow parameters and pipe geometry structure. In this study, the airflow flow law of the multi-branch pipeline of the pneumatic system was studied, the mechanism of airflow flow in the multi-branch pipe was analyzed, and it was clarified that the main factors affecting the airflow flow in the pipe, namely, air density, air dynamic viscosity, the total flow rate of the inlet branch pipe, the length of the closed end of the header, the inner diameter of the outlet branch pipe, and the outlet branch pipe spacing. Numerical simulations were carried out using Fluent simulation software to elucidate the cause of multi-branch pipes of uneven distribution of airflow in multi-branch pipes, the empirical equation among these factors and the flow velocity of the outlet branch pipe are established by dimensional analysis method. The bench test results show that the established empirical equations are applicable in the following ranges: 0.018 m3/s <= Q <= 0.054 m3/s, 0.045 m <= d <= 0.05 m, 0.075 m <= L <= 0.125 m, 0.7 m <= Y1 <= 0.875 m (0.5 m <= Y2 <= 0.75 m, 0.36 m <= Y3 <= 0.45 m), the prediction accuracy can be controlled within 10% of the empirical formula, which can provide a reference for the prediction and optimization design of outlet velocity of the multi-branch pipe.

为探究气吸式播种机气力系统多分支汇流管路负压气流的流动规律,掌握管路总体压力损失与管路几何结构之间的关联特性,获取管路总体压力损失的定量预测目标值,该研究对多分支汇流管路气流流动状态进行分析,明确了影响管路气流流动的主要因素,采用单因素试验及Fluent仿真模拟,从宏观、微观尺度阐明多分支汇流管路中的气流流动规律及总体气压损失原因,通过量纲分析法建立了总体压力损失(ΔP,Pa)与空气密度(ρ,kg/m3)、空气动力黏度(μ,Pa·s)、集管封闭端长度(L,mm)、入口支管1的入口流量(Q,m3/s)、入口支管内径(d,mm)、入口支管长度(h,mm)、入口支管间距(δ,mm)、集管内径(y,mm)、出口支管内径(D,mm)和出口支管长度(Δ,mm)关系的经验式.台架试验结果表明,所建立的经验式应用范围为0.0009 m3/s≤Q≤0.0045 m3/s,28 mm≤d≤45.2mm,100 mm≤l≤200 mm、200 mm≤δ≤300 mm,42.6 mm≤y≤81.4 mm,150 mm≤Δ≤250 mm,34 mm≤D)≤42.6 mm、53.6 mm≤D≤57 mm,对多分支汇流管路总体压力损失的预测精度在经验式计算值的10％以内.所建立的经验式可为气吸式播种机多分支汇流管路的设计选型、结构优化提供参考.

为了适应杂交水稻的多样性,以及满足杂交稻精量播种的要求,该研究结合水稻气力式播量可调排种器设计了一种水稻气力式播量可调穴播机.该穴播机采用独立风机为排种器提供气源,根据排种器气压需求,设计了单段式管路与双段式管路,并进行对比试验分析,试验结果表明,双段式管路能更加均匀的分配气压,且双段式管路气压的变异系数小于5％.采用杂交稻五优1179为试验对象,在不同的吸种负压下,进行不同播量的田间试验研究,试验结果表明:当2孔工作时,最佳吸种负压为2.0 kPa,平均播种合格率为:93.35％;当3孔工作时,最佳吸种负压为1.6 kPa,平均播种合格率为:87.21％;当4孔工作时,最佳吸种负压为1.6 kPa,平均播种合格率为:83.73％;当5孔工作时,最佳吸种负压为1.6 kPa,平均播种合格率为:79.86％.该研究分析了影响田间播种的主要影响因素,且由试验可得,该机可满足田间播量可调的需求,为实际的生产应用提供了一定的基础.

In order to improve the single-grain seeding rate of the pneumatic single seed metering device, an airflow seed cleaning device was designed in combination with positive pressure airflow. The influence of the position of the seed cleaning mechanism on the seed cleaning effect is theoretically analyzed and a flow field simulation test analysis of different nozzle structures was carried out by using Fluent software (ANSYS, Inc., Canonsburg, PA, USA). The results of this test show that a nozzle with a Witoszynski curve has good airflow concentration and uniform air pressure distribution. In order to verify the performance of the seed cleaning mechanism, a 0.7 times coated seed (hybrid rice Wuyou 1179) was used as the test material and a quadratic regression test with three levels was carried out with the rotation speed of the seed plate, the negative pressure of the suction chamber, and the positive pressure of the seed cleaning as the test factors. The results showed that when the speed of sucking plate was 30 r/min, the negative pressure of the suction chamber was 1.8 kPa and the positive pressure of the seed cleaning was 0.2 kPa; the seeding effect was at its best and the qualified rate of the seed metering device was the highest at 86.43%, the minimum leakage rate was 3.81%, and the multiple rate was 9.76%. The proposed seed cleaning mechanism effectively improves the accuracy of seeding and provides a certain theoretical basis for the single-grain sowing of hybrid rice.

为满足杂交稻单粒播种的作业需求,该研究结合包衣稻种设计了一种单粒气力式排种器,分析了吸种姿态对吸种精度的影响,利用稻种导流原理,设计了一种导流式吸种盘,对稻种在该吸种盘导流作用下的运动过程进行了分析,建立了吸附过程中稻种与吸种盘之间的运动模型.采用包衣稻种(杂交稻五优1179)为试验材料,采用三因素三水平全因素试验方法,在不同吸种盘转速、吸室负压和吸种盘结构情况进行试验分析.试验结果表明:在转速30 r/min、吸室负压1400 Pa时,有导流槽和辅助吸种装置的吸种盘吸种效果最佳,单粒吸种率最高为81.58％,漏吸率为2.89％.试验结果验证了该吸种盘可有效提高单粒吸种率,满足杂交稻单粒播种的作业需求,为杂交稻单粒播种提供了一定理论基础.

[目的]小粒种子具有尺寸小、质量轻、形状不规则的特征,采用传统排种器作业时常发生吸种孔堵塞、种子损伤、播种均匀性差的问题;因此本研究在种子丸粒化技术的基础上设计了一种气吸式小粒种精量穴播排种器.[方法]通过测量种子的尺寸大小和摩擦角等相关参数,采用Rocky离散元仿真软件对进种过程进行仿真模拟.为获得该排种器的最佳性能因素组合,进行了二次回归旋转正交试验,应用多目标优化方法对排种器性能影响因素进行优化.[结果]通过回归系数的检验得知,影响排种器单粒率与空穴率的因素主次顺序为气压、排种器转速.当转速一定时,随着负压的增加,单粒率随之增加,空穴率随之降低,当负压一定时,随着转速的增加,单粒率随之降低,空穴率随之增加,当负压大于?2800?Pa时,转速在5～30?r/min的范围内对排种器单粒率和空穴率影响不明显,且此时单粒率均在90％以上、空穴率均在10％以下.[结论]通过优化求解,最优工作参数组合为转速15?r/min、负压?2300?Pa、正压500?Pa.经试验验证,在此条件下该排种器的性能指标为单粒率合格指数平均值96％、漏播指数平均值3.37％、重播指数平均值0.267％,符合国家标准要求.

To adapt to the diversity of hybrid rice and meet its requirements of precision seeding, a rice pneumatic seeder with adjustable seeding rates was designed in this study. The seeder employed an independent vortex pump to provide the air source for the seed metering device. According to the requirements of air flow in the seed metering device, a sub-pipeline and a general pipeline were designed. The performances of the two types of pipelines were verified by the air pressure uniformity tests. The results showed that the sub-pipeline can distribute the air pressure more evenly than the general pipeline. The coefficient of variation of the sub-pipeline pressure was less than 5%. Wuyou 1179 hybrid rice was selected as the experimental object. The field seeding tests were carried out with different negative pressures and different number of groups of sucking holes as experimental factors. The results showed that the average qualified rate of seeding was 93.35% when only 2 groups of sucking holes were working under the seed sucking negative pressure of 2.0 kPa. The average qualified rate of seeding was 87.21% when 3 groups of sucking holes were working under the seed sucking negative pressure of 1.6 kPa. The average qualified rate of seeding was 83.73% when 4 groups of sucking holes were working under the seed sucking negative pressure of 1.6 kPa. The average qualified rate of seeding was 79.86% when 5 groups of sucking holes were working under the seed sucking negative pressure of 1.6 kPa. The main factors affecting the seeding effect were analyzed and the feasibility of a rice pneumatic seeder with adjustable seeding rates was verified by field tests. The research results can provide a basis for its practical production and application. Keywords: agricultural machinery, adjustable seeding rate, seeder, pneumatic, rice, pipeline DOI: 10.25165/j.ijabe.20211404.5658 Citation: Xing H, Wang Z M, Luo X W, Zang Y, He S Y, Xu P, et al. Design and experimental analysis of rice pneumatic seeder with adjustable seeding rate. Int J Agric & Biol Eng, 2021; 14(4): 113–122.

Rice seeding in hill is beneficial to the growth of rice in the field and the increase of rice yield. However, rice seed metering device usually uses multiple rice seeds for sowing, which is difficult to form a hill. To improve the performance of rice seeding in hill, the seed throwing mechanism of the rice pneumatic seed metering device with adjustable seeding rate was study, and the trajectory of seed throwing was analyzed theoretically. The equation of seed throwing trajectory was established. The distribution of sucking holes on the sucking plate was optimized by using asynchronous seed throwing method. The distribution mechanism of seed throwing was studied, and the theoretical trajectory area of seed throwing was established. The actual trajectory area of seed throwing was established by high-speed photography. The theoretical area and actual trajectory area of seed throwing were compared by experiments. The influence factor of errors between the actual and theoretical seed trajectory areas were analyzed. The performance of seed throwing in hill was tested under different positive pressure and different rotational speeds. The optimum qualification rates of different seeding rates were 97.34%, 90.36% and 87.36% respectively. These were 10-17% higher than the original qualification rates of seed throwing. The experimental results showed that the optimized sucking holes on sucking plate could effectively improve the performance of seeding in hill of seed metering device. This study provided a theoretical basis for the seed throwing mechanism of the rice pneumatic seed metering device, and improved the qualification rate of seed throwing.

[目的]为了改善水稻气力式排种器工作时稻种的重吸附现象,设计了一种垂直于排种盘平面的清种装置.[方法]对水稻气力式排种器工作时稻种的受力与清种装置的工作原理进行了分析,建立了吸种过程中的受力模型.采用超级杂交稻'五丰优615'为试验对象,在有、无清种装置的条件下进行了排种器的精度试验.在吸室负压为4.0 kPa的条件下,进行了清种块厚度和排种盘转速的两因素试验分析.[结果]采用清种装置后,1～3粒/穴的占比由62.02％ 提升至90.00％ 左右,≥4粒/穴的占比由37.98％ 降至5.00％,改进效果较为明显.当清种块厚度为3.5 mm、排种盘转速为15、20和25 r/min时,1、2和3粒/穴的占比分别为95.18％、95.16％ 和95.23％,空穴率分别为2.07％、2.76％ 和4.56％,满足超级杂交稻的田间播种需求.[结论]当吸室负压一定时,降低排种盘转速可以提高清种装置的清种效果,提高排种器的播种精度.本文针对水稻气力式排种器的结构,设计了一种清种装置,有效地清除了排种器重吸附的稻种,为提高水稻气力式排种器的精度提供了依据.

为了满足杂交水稻播种量不同的要求,该文设计了一种水稻播量可调气力式排种器,对其工作原理进行了分析,对关键部件进行了参数设计,该排种器采用多个相互独立的负压流道对吸种精度进行控制.利用ANSYS-FLUENT有限元流体分析软件对负压流道结构的吸孔负压影响规律进行了分析,优选了最佳流道结构.选取超级杂交稻Y-2优900为试验材料,进行了不同播种量下吸室负压、排种盘转速与排种盘吸孔组数对播种精度的影响试验研究,试验结果表明:当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为20 r/min时,1孔播种达到最佳效果,合格率为82.41％;当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为40 r/min时,2孔播种达到最佳效果,合格率为96.36％;当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为20 r/min时,3孔播种达到最佳效果,合格率为92.79％;当吸孔组数为16、吸种负压为1.2 kPa和排种盘转速为20 r/min时,4孔播种达到最佳效果,合格率为91.93％;当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为30 r/min时,5孔播种达到最佳效果,合格率为87.88％.说明水稻气力式播量可调排种器可满足杂交稻在采用直播式时不同播量的要求,相比于原有的排种器更佳适应水稻的多样性.该研究可为水稻机械化穴直播技术提供了参考.