| Seeding device is the key equipment to precision seeding, the quality of seeding is related to high quality and high yield directly. Presently, the seeding device of super rice is still at the exploratory stage, the seeding device of rice used wildly are mechanical type, which cause a more serious seeds injury, only meet seeding3-5seeds per hole,and difficultly to meet the super rice planting on seeding agronomic requirements(2±1seeds per hole, little seeds injury). Therefore, study on theory of super rice plug seedling precision seeding device is become a more urgently needed. The research takes new designed vacuum-vibration tray precision seeding device as object, through vibration theory, computational fluid dynamics, discrete element method, mechanism, experimental optimization theory, deeply study mechanism motion, the law of seed group vibration excitation and pneumatic strength to super rice particle in seeding process, combined with advanced computer simulation technology, parameter combination in the continuous seeding process of optimal suction seeds effect, put forward to precision seeding theory, the major research work as follows:(1) Make measurement and analysis three types of super rice sprout basic physical parameters change by professional measurement instruments:get three-axis geometry size distribution probability, thousand-grain weight, density, friction coefficient, repose angle, the recovery restitution and force-displacement changing process of super rice sprout. Provided the basis for the discrete element simulation and suction component designing of seeding device.(2) Study flow field of seeding device by FLUENT:①Analysis flow field distribution law of suction plate, get main factors which affecting flow field are suction hole’s aperture, vacuum negative pressure value, obtain the optimal structure and working parameters of the uniform stability flow field.②Analysis influence factors of seed particle force in flow field, the primary-secondary order is:the distance seed and suction hole, seed attitude, vacuum negative pressure value, suction hole’s aperture; set up seed force mathematical model, and then get:vacuum negative pressure value and suction hole’s aperture should be reasonable matching, small aperture need larger vacuum negative pressure, height direction of seed is most easily adsorbed; vacuum negative pressure value is in the range of3-5kPa, when suction hole’s aperture is1.5mm～2.0mm, suction pore distance range is from0.34mm to1.90mm.③Simulate the suction plate of air flow field, get flow effect to the suction plate air flow, with increasing of flow, with the seed force increasing by air blowing,suction orifice flow velocity increases rapidly, effect of inner plate thickness on the positive pressure air flow distribution and flow is little.④Test flow of field flow and seed particles adsorption, test results and FLUENT simulation results are in good agreement, which shows that the correctness of numerical simulation results.(3) Carry out mechanism kinematic analysis of seeding device.①Study on vibration plate motion by ADAMS, get the change of mechanism’s power:with the increasing of frequency and amplitude, maximum driving torque increases.②Based on mechanism theory of parallel mechanism, study parallel mechanism with level adjustment requirements, carry out type synthesis of a translation two rotation parallel mechanism, design a horizontal adjusting mechanism, get the relationship between the position and the accuracy model.③Analysis seed particle force and build the seed particle force model, get the dynamic characteristics of suction disc movement requirements. With the increasing of pressure, the critical acceleration of manipulator increases. Seed most easily falling at the length of seed adsorption, manipulator design should satisfy the length direction falling condition that does not occur.④Study on seed particles and suction plate collision movement, establishing collision motion model, get the relationship between seed particles is not touched off the bounce of critical velocity and negative pressure suction panel values. With the pressure increase, the critical velocity of seed particles increase. The length of seed is most likely to occur collision bounce off, when the impact velocity is greater than the critical speed, the seed will be out of flow field constraints and bounce off suction hole.(4) Based on the theory of discrete element method, study seed group movement in vibration plate, get:①Movement of the single seed has fluctuation, seed group movement changes regularly without obvious fluctuations, the reason is that the formation of constraint forces between seeds particles.②With the increase of vibration frequency and amplitude of plate, the average displacement of seeds, the average velocity and the particle force of Z direction gradually increases, throwing motion of seeds increase fiercely, relative spatial distribution density becomes smaller gradually, increasing frequency and amplitude can increase throwing height of seeds effectively. Average normal force and average tangential force of single layer thickness, is larger than other kinds of thickness seeds which Z direction average displacement, average velocity and particle force is closed, spatial discrete of seeds is similar. Maximum force of seed particles are less than0.03N, vibration plate has minimal damage to seed.③Study on parameters relationship between thickness and vibration of seeds that seed of variable mass system gradually reduce in seeding process, establish mathematical models between device parameters and suction distance(the distance between the panel and layer surface). The effect order throwing height of seeds is: vibration frequency, amplitude, layer thickness. get vibration frequency and amplitude shoould be reasonable matching; simulation for plate tilt state seeds movement, when the plate angle is large, seeds movement uniformity is worse, tilt angle is smaller, the space vibration of seeds distribution uniformity is more favorable.④Based on the theory of CFD-DEM coupling, simulate suction process of seeding device, get the variation of parameters.(5) Designing a new type of vacuum-vibrating tray precision seeding device test bed, carrying out bench test①Single factor test and orthogonal experiment, emphatically analysis vacuum negative pressure value, suction hole’s aperture, vibration frequency of plate, amplitude,the suction distance on effects of seeding performance. Get the primary-secondary order of the factors affecting qualified rate are:the suction distance, vibration frequency, amplitude, vacuum negative pressure value, suction hole’s aperture Get the primary-secondary order of the factors affecting rebroadcast rate are: vacuum negative pressure value, suction hole’s aperture, the suction distance, vibration frequency, amplitude. Get the primary-secondary order of the factors affecting cavity rate are:the suction distance, vacuum negative pressure value, suction hole’s aperture, vibration frequency, amplitude. The suction distance and frequency had significant effects on the pass rate of seeding, vacuum negative pressure value and suction hole’s aperture had significant effects on rebroadcast rate, the suction distance and vacuum negative pressure value had a significant effects on cavity rate.②Establishing a mathematical model between seeding device parameters and seeding performance index, made multiobjective optimization genetic algorithm, get the optimal solution:vacuum negative pressure value is3.68KPa, suction hole’s aperture is1.84mm, vibration frequency is10.90Hz, amplitude is4.09mm, the suction distance is3.92mm, and which verified by experiments.③Through seeding test of different kinds of super rice, which showed that the seeding device has a good adaptability to different varieties of super rice, which are suitable for different varieties of super rice seeding. Through seeding seedling test which showed that the seeding device can meet the requirements of super rice plant. Seeding test by seeding device, statistics after sowing budding condition. The seeding device does not hurt bud, and meet requirements of super rice planting seedling.The results are consistent with theoretical analysis, and provide a theoretical basis for precision seeding device’s designing. |
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