| Seedling transplantation can compensate the climate and improve the comprehensivebenefit to crop growth in early. However, because of dry land transplanting machinery developsslowly in China, transplanting is still mainly manually performed, even the mechanicaltransplanting rate of cotton is less than30%, which in fact has the highest degree ofmechanization. With the vigorous development of China’s profitable agriculture, transplanter thatcan achieve a high seedling erectness rate and low damage rate in high speed has become thetrend of development. Transplanting mechanism is ultimate mechanism that has seedling plantedin the field, it is one of the two core mechanisms of the transplanting machine, whose behaviordirectly affects the performance and competitiveness of the whole transplanter. Therefore, thetheoretical and experimental research on transplanting mechanism, which can provide thetheoretical basis and design basis for the research and development of high speed transplanter,has important practical value and theoretical significance.The ideal requirements of planting mechanism are high seedling erectness rate and lowdamage rate in high speed. The traditional planting concept "zero-speed" is very difficult toachieve those goals in actual practice, and the traditional transplanting mechanism can not meetthe high-speed transplanting requirements either. Aiming at these problems, this paper putsforward one kind of new ideas that by ensuring the kinematic characteristics of desired trajectory,gesture, velocity of planting nozzle and the shape of the opening to improve the seedlingerectness rate and reduce the damage rate, and under the guidance of this idea, research ontransplanting mechanism based noncircular gear planetary transmission was carried out. Themain research contents and results are as follows:1) Study the working principle of various types of transplanting mechanism both home andabroad, and analyze their problems. Summarize the requirements for planting mechanism thatcan meet the condition of high seedling erectness rate and low damage rate. Thus transplantingmechanism of non-circular gear planetary transmission was proposed in this paper. Mechanismsynthesis was carried out according to the different types of non circular gear (noncircular gearof ellipse, eccentric-circle, Fourier plot, Pascal curve) transmission.25different types oftransplanting mechanism was proposed in total. On the basis of the analysis of noncircular gearpair transmission characteristics, the kinematics and dynamics models of the transplantingmechanism were established. Kinematics and dynamics auxiliary analysis software was alsodeveloped, getting the kinematics and dynamics characteristics of transplanting mechanism.2) In order to reveal the mechanism of seedling’s injury, broccoli was chosen as the researchobject, an orthogonal test was designed to study the mechanical characteristics of broccoli seedling with different tray specifications, different water content and different ages, includingthe anti-press strength of soil bowl, the friction coefficient between seedling and planting nozzlewall, and the relative velocity which keeps the seedling do not rebound after colliding theplanting nozzle. Analyze the influence of these factors imposed on the seedling injury, using thecomprehensive evaluating method and considering in financial terms, the physical characteristicsof broccoli seedling were obtained which were suitable for mechanical transplanting operation:128hole plate,5~6leaves, water content of50%and128hole plate,2~3leaves, water content of63%, and they provide a basis for the subsequent construction of ideal gesture of planting nozzleand speed of plant operation.3) Analyze the relative movement in the process of transplanting between seedling andplanting nozzle, combined with the kinematics model of transplanting mechanism and thephysical and mechanical properties of broccoli seedling, the differential equations of seedling’smotion relative to the planting nozzle was established, kinematics aided analysis software wasdeveloped, and get the kinematics characteristics of broccoli finally.4) Using the physical and mechanical properties of broccoli seedling as the constraintconditions, and combining with the agronomic requirements, theoretical model of desiredtrajectory, gesture, velocity of planting nozzle and the shape of the opening in one working cyclewas built. A multi-objective optimization model of kinematic characteristics of plantingmechanism aimed at ideal kinematic characteristics was established, based on the kinematicmodel of planting mechanism and the kinematic differential equations of broccoli seedling.Using Matlab genetic algorithm toolbox to optimize each kind of non-circular gear planetarysystem transplanting mechanism, finding the parameter range that can meet kinematicscharacteristics requirement for each transplanting mechanism.5) Based on the dynamics model established before, the criteria for evaluation of dynamiccharacteristics were constructed, based on kinematic optimization results as constraint conditions,dynamic multi-objective optimization model was established. The best type of transplantingmechanism and its corresponding parameters were obtained by similarly using the geneticalgorithm for dynamic optimization: the eccentric type of non-circular gear was used as the firstgear pair, and the elliptical non-circular gear was used as the second gear pair, the mechanismparameters are as follows: the initial installation angle of planting nozzle θ=114.256, theangle between the center line of two non-circle gear pair γ=30.834, the initial phase angle ofgear3α=25.467, the initial phase angle of gear6β=1.375, the eccentric circle radius of thesun gear3R3=30.916mm, the offset of sun gear3e3=5.583mm, the deformation coefficient of sun gear3m31=1.542, the radius of ellipse major axis of mid-gear6A6=30.694mm, theeccentricity ratio of mid-gear6k6=0.031, the deformation coefficient of mid-gear6m61=1.26.6) The structure of the mechanism was designed according to the optimum type and thecorresponding optimized mechanism parameters offered by the optimization, and3D model wasbuilt; Test stand has been developed, it can test the kinematics(trajectory, velocity) and dynamiccharacteristics of the transplanting mechanism under the condition of no-load, verifying thecorrectness of the established mathematical model; experiment of simulating the field plantingwas conducted on the rotating test stand, testing the effect of space, depth, specification ofbroccoli seedling,seedling stage and the rate of water content that was composed on the fieldoperation performance of transplanting mechanism. The results showed that the seedlingerectness rate could reach a comparative high level about95%when it met the followingcondition: the space was about280mm~380mm, the depth was about45mm~55mm,128holeplate,2~3leaves, water content of63%. |
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