| Leafy vegetables such as spinach are planted in a narrow row and dense planting mode.By increasing the number of plants per unit area,the plants can give full play to their yield advantages under reasonable density.This research endeavors to address the challenges associated with small-sized vegetable seeds,specifically spinach,when employing narrow-row dense planting techniques.These issues encompass strict uniformity requirements for high seed viability rates and a lack of compatible seeding technologies and equipment.In response,a novel low-position precision seeder was developed,which integrates rotary tillage ridging,ditching,seeding,soil covering,and additional functions,all optimized for narrow-row dense planting.The design and parameter matching of multi-row parallel low-position seeding device and narrow-row ditching assembly device were carried out.The kinematics simulation of the seeding process and the discrete element simulation of the ditching process were studied,and the performance of the test machine was verified in the field.This study mainly carried out the following work:(1)The overall design of narrow-row close planting low-seeding precision seeder was carried out.According to the agronomic requirements and related technical difficulties of narrow-row dense planting,a narrow-row dense planting low-position precision seeder was designed to realize the narrow-row precision seeding operation on the ridge of high-economic leafy vegetables.The structural composition,operational principles,and primary technical parameters of the seeder were established.According to the ridge requirements of dense vegetable planting,the ridge width was 1000 mm,the ridge bottom width was 1200 mm,the ridge height was 150～200 mm,and the working speed of the seeder was 0.2～0.6 m/s.(2)The design and analysis of multi-row parallel low-position seeding device were carried out.A multi-row parallel low-position precision seeding device with planetary gear train seeding mechanism was designed.The configuration and operational methodology of the seeding device were explicated.By means of the collaboration between the planetary gear train mechanism and the air distribution pipe suction needle,enhancements were made to the original motion trajectory of the suction needle.The relative motion speed of the suction needle and the seed was reduced during the suction,and the height of the seed and the seed bed was reduced during the seeding to improve the seeding performance.A mechanical model was formulated to explicate the processes of seed suction and throwing,subsequently allowing for the identification of the primary structural parameters for the seed metering device.The structural parameters for both the solar and planetary wheels within the planetary gear train mechanism were also ascertained.The diameter of the air distribution tube was determined to be 20 mm,the diameter of the suction needle was 10 mm,the diameter of the suction needle hole was 2.0 mm,the length of the suction needle was 95 mm,and the spacing between adjacent suction needles was 75 mm.The initial installation positions of the suction needle on the planetary wheel and the air distribution tube were-90°,0°,90° and 180°.The ADAMS simulation technique was employed to examine both the static and dynamic trajectories of the suction needle within the metering mechanism of the planetary gear train.Combined with the displacement curve and the velocity curve,the motion law of the suction needle of the metering device and the conditions for the metering device to achieve high-low-speed suction and low-zerospeed seeding were explored.The negative pressure area of the air chamber was 300°,and the positive pressure area was 60°.(3)A performance evaluation of the seed metering device was conducted.The outcomes of a single-factor experiment indicated that,at a negative pressure of 2.0 k Pa and positive pressure of 1.0 k Pa,the qualified index initially increased and then decreased with an increase in the seeding shaft’s rotational speed.When the seeding speed ranged from 18-22 r/min,the qualified index was above 90%.Furthermore,the results of an orthogonal experiment involving three factors and five levels revealed that a seeding speed of 19.56 r/min,suction negative pressure of 2.05 k Pa,and unloading positive pressure of 1.00 k Pa resulted in superior seeding performance,with a corresponding seeding qualified index of 90.92%,missed seeding index of 4.98%,and replay index of 4.10%.The best parameter combination is : the rotation speed of the seeding shaft is 20 r/min,the negative pressure of the suction is 2.0 k Pa,and the positive pressure of the unloading is 1.0 k Pa.In order to test the effects of seeding speed,unloading positive pressure and seeding height on the uniformity of plant spacing,seeding experiments were carried out.The results showed that under the same positive pressure of seed unloading,when the seed height increased from 100 mm to 200 mm,the variation range of seed spacing variation coefficient was relatively small.When the seeding height increased to 300 mm,the interval of seed spacing changed greatly,and the coefficient of variation of seed spacing increased to more than 17.0%.When the seeding positive pressure of is maintained within the range of 0.8～1.0 k Pa,coupled with a working speed between 18～20 r/min,and a seeding height below 200 mm,the variation coefficient of seed spacing is found to be less than 13.2%,thereby leading to improved working performance.(4)The design and test of narrow row close planting ditching assembly were carried out.A narrow-row dense planting ditching assembly used in combination with a multi-row parallel low-seeding metering device was designed.The structure and working principle of the narrow-row dense planting ditching assembly were described.Combined with the working process and mechanical kinematics analysis of the discslider combined opener,the structure and key parameters of the opener disc and the slide-type soil separating plate were determined.The diameter of the spherical disc was determined to be 200 mm.In order to ensure that the soil particles cut by the slide-type soil separating plate slide backward along the main body of the soil separating plate,the inclination angle of the soil separating plate was determined to be less than 30°.The study investigated the dynamics of seed movement and migration trajectory during the seeding process,which facilitated the determination of the structural characteristics and dimensions of the lower seed tube.Specifically,the lower seed tube was found to possess a rectangular interface,measuring 50 mm in length,25 mm in width,and 100 mm in overall height.Moreover,the investigation of seed ditch was carried out by conducting a discrete element simulation analysis using EDEM.Taking the ditching depth,the inclination angle of the sliding knife type soil plate and the working speed as the test factors,the soil disturbance amount and the coefficient of variation of the ditching depth as the test indexes,the quadratic regression orthogonal combination test was carried out.The optimal combination of the parameters of the opener was 45.45 mm,the inclination angle of the sliding knife type soil plate was 20.14°,and the working speed was 0.40 m/s.(5)A field experiment involving the use of a narrow row close planting lowposition precision seeder was carried out,and the qualified index of the field verification test was determined to be 92.2%.The coefficient of variation of grain spacing was found to be 10.8%,which was consistent with the conclusion of the bench test.The average ditching depth of the ditching verification test was 39.0 mm,and the coefficient of variation of ditching depth stability was 10.04%.The field sowing test indicated that the optimal parameter combination led to a coefficient of variation of the number of seedlings per row and the consistency of the number of seedlings per row of less than 10%,which satisfied the agronomic requirements for narrow row and dense planting of small-sized vegetable seeds. |
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