Research On Pneumatic Cylinder-type Precision Seed-metering Device For Rice

The rural labor force changed from the seasonal shortage to the annual shortage with the adjustment of the social industrial structure. The paddy rice planting pattern of transplanting whose cost increases heavily take more time and labor force. At the same time, the practical questions of agricultural fresh water resources’ shortage and so on have limited the transplanting pattern of paddy rice. Compared with paddy rice transplanting, the direct seeding of paddy rice have more obviously advantages, such as saving work,water and cost, with high efficiency. The direct seeding area of paddy rice increases year by year, and the hybrid rice varieties suitable for direct seeding generalizes constantly. The requirement of advanced and reliable seeding equipment that have excellent performance and suitable for precision hill direct seeding of hybrid rice is more urgentAiming at the practical problem of rice direct seeding equipment can not realize the agronomic requirement that every hill needs 2~4 seeds while direct seeding of hybrid rice. In order to solve this problem, a precision hill dropping seed metering device was designed,which combines socket filling seed, multiple suction holes absorbing seeds, air blowing cleaning seeds with flexible rope assisted, follow-up belt protecting seeds and pneumatic clear blockage of suction holes. The seed metering device adopts bigger size of socket to fill seeds, multiple suction holes to absorb quantitative seeds, and air blowing to clean and fix seed,which could meet the hole number and hole distance requirement of precision hill dropping for hybrid rice in field. The seed metering device’s multi-line seeding function is conducive to solve the problems of overall bloated of seeder taken by single seed metering device, pneumatic distribution system, higher power of fan power and so on. The home and abroad research status of pneumatic metering device was elaborated and summarized in the paper. Aiming at the agronomic requirement of hybrid rice direct seeding, adopting the method of combining theory and practice to explore and study pneumatic cylinder-type precision direct seed-metering device for rice. The main contents include:(1)The research object were Huang Huazhan, Shan You 63 and Gang You 364, which were suitable for planting in the field of middle and lower reaches of the Yangtze River. The experiment researched the main physical characteristics of rice bud seed under the normal moisture content of its growth, which contains three axis size,weight of one thousand seeds,sliding friction angle, repose angle, suspension velocities and so on. The experiment of rice bud seeds’ survival rate after being compressed was done. The solution of these problems provided basic data for designing the key part of seed-metering device and choosing the working parameters.(2)According to the direct seeding agronomic requirement of hybrid rice, a pneumatic cylinder-type precision direct seed-metering device which could realize multi-line seeding was designed. The seeding pattern of filling seed by bigger size sockets, absorbing seeds by multiple suction holes and cleaning seeds by air blowing was put forward firstly. The paper analyzed and determined the structural parameters of the key part of seed-metering device, designed3 different sockets to filling seeds for different hybrid rice and did seeding performance experiment in order to choose a better socket for seeding. What is more, the seeding suitable experiment for different hybrid rice by the better socket has been done.(3)The paper adopted engineering mechanics, fluid mechanics, aerodynamics and so on to analyze and experiment study the seed filling, seed absorbing, seed clearing, seed carrying, seed dropping and suction hole cleaning process of pneumatic cylinder-type precision direct seed-metering device. The dynamic and kinematic models of rice bud seed in seeding process were built and the seeding principle of metering device was determined in the paper. The paper also analyzed and calculated the critical negative vacuum degree for seed absorbing, critical positive vacuum degree for suction holes clearing and other main working parameters. The seed clearing process of flexible rope and the seed dropping process of metering device were cleared by means of the high-speed camera technology. The paper analyzed the time of seed clearing process by flexible rope, and determined that the seed clearing process of flexible rope had no damage to rice bud seeds. The paper determined the seed dropping track clearly and confirmed the correction of seed dropping analysis. The main structure and size of seed spout of seed-metering device designed and determined respectively according to the actual dropping track in the paper.(4)Through theoretical analysis and calculating, the airflow field in negative pressure zone, positive pressure zone, and shunt-tube were determined under turbulence state, and the gas in the 3 airflow fields were all for incompressible. With the experimental evaluation indexes of the average turbulent kinetic energy of airflow field and the average pressure or velocity of key parts, the simulating optimizations of the 3 airflow fields of seed-metering device were launched by using the CFD simulated analysis software CFX.(1)The response surface simulation experiment of flow field in negative pressure zone indicated that the order affecting the average pressure of the 3 suction holes end face in socket was outlet diameter of negative pressure chamber > suction hole diameter >axial distance between two sockets, and the order affecting the average turbulent kinetic energy of flow field was suction hole diameter>outlet diameter of negative pressure chamber>axial distance between two sockets. Full factorial quadratic regression model equations between the response indexes and experimental factors were constructed. Through the variance analysis of experimental results, the significant affecting on experimental factors on performance evaluation indexes has been determined. The optimal structural parameters of the negative pressure zone of seed-metering device were 1.4 mm suction hole diameter, 22 mm outlet diameter of negative pressure chamber, and 34 mm axial distance between two sockets, and that was obtained by optimization solution the regression equation of performance evaluation indexes in the range of experimental parameters constraints. The results of verification test were consistent with the results of optimization solution. Under the condition of the optimal structural parameters and with-3000 Pa outlet of negative pressure chamber, the average pressure of the 3 suction holes end face in socket was-1428.14 Pa, and the average turbulent kinetic energy of flow field in the negative pressure zone was 0.472 m2·s-2. The pressure and velocity contour of flow field of verification test indicated that the distribution position design of the 3 suction holes was reasonable.(2)The full factorial simulation experiment of positive pressure zone of metering device made clear that the inlet diameter of positive pressure chamber and the interactions between size of chamber and inlet diameter of chamber had significant influence on average turbulent kinetic energy of flow field in positive pressure zone and average pressure of the 3 suction holes end face in chamber. The optimal combination structure parameters of positive pressure chamber were determined by analysis the simulation result, and the optimal combination was L type chamber with 22 mm inlet diameter. Under the optimal combination and with 500 Pa inlet of positive pressure chamber, the average pressure of the 3 suction holes end face in chamber was 195.75 Pa, and the average turbulent kinetic energy of flow field was 0.129 m2·s-2.(3)The simulation contrast test of different structural styles of seed clearing flow shunt-tube indicated that II type and III type shunt-tube could effectively improve the uniformity consistency of the average velocity of the 4 seed clearing air nozzles, although the friction loss of flow in tube increased and the average velocity of 4 air nozzles were slightly smaller due to one more vertical shunt of flow in tube, compared with I type and IV type, and improving uniformity consistency was beneficial to enhance the overall seed clearing performance of metering device. In order to obtain the uniform stable seed clearing flow velocity of the 4 air nozzles, the II type shunt-tube should be priority used to ensure a well seed clearing performance of metering device.(5)The paper launched indoor bench experiment of pneumatic cylinder-type precision direct seed-metering device for rice and studied the relationship between seeding performance and cylinder speed, vacuum degree, air-blowing velocity and clearing blockage positive pressure of chamber.(1)The result of single factor experiments indicated that seeding cylinder speed,vacuum degree and air-blowing velocity had significant influence on the qualified rate, miss-seeding rate and reseeding rate of metering device respectively. The clearing blockage positive pressure of chamber had no significant influence on qualified rate, miss-seeding rate, reseeding rate, the average holes distance and the variation coefficient of holes distance of metering device respectively. During the seeding work, we should provide definite strength of clearing blockage positive pressure to ensure suction holes cannot be blocked by impurities. When the seeding cylinder speed was in range of 10~20 r/min, vacuum degree was in range of 3~5 kPa, air-blowing velocity was in range of 12.22~22.98 m/s, and clearing blockage positive pressure was in range of 750~1250 Pa, the seeding performance of metering device was well, and its qualified rate could reach more than 85%, respectively. Under the condition of seeding cylinder speed with 10 r/min,vacuum degree with 4.0 kPa, air-blowing velocity with 17.60 m/s and clearing blockage positive pressure within range of 750~1250 Pa, the seeding performance was excellent, the qualified rate could reach more than 85%, miss-seeding rate lower than 6%, reseeding rate lower than 10%, respectively.(2)The three factors and five levels quadratic regression rotation design optimization experiment of metering device made clear that the order affecting qualified rate was seeding cylinder speed>vacuum degree>air-blowing velocity, and the order affecting miss-seeding was vacuum degree>seeding cylinder speed>air-blowing velocity. The variance analysis of experimental results determined significant affecting of experimental factors on performance evaluation indexes. The optimal combination working parameters of metering device were seeding cylinder with 10 r/min, vacuum degree with 4.6 kPa and air-blowing velocity with 21.88 m/s, and that was obtained by optimization solution the all factors quadratic regression model equation of performance evaluation indexes in the range of experimental parameters constraints. The results of verification test were consistent with the results of optimization solution. Under the condition of the optimal combination working parameters, the qualified rate, miss-seeding rate, cavity rate and reseeding rate were 87.73%, 2.93%, 0.53% and 9.33%, respectively. Meanwhile, the seed breakage rate was 0.89%, the average hole distance was 200.07 mm(theoretical hole distance was 200 mm), the variation coefficient of hole distance was 4.75%, the apiece row consistency variation coefficient of seeding quantity was 4.24%, the stability variation coefficient of the full seeding quantity was 4.11%, and this seeding quality meet the direct seeding requirements of hybrid rice.