| Mechanized pot seedling transplanting can not only alleviate the contradiction of crop stubble and expand the planting area,but also improve the survival rate,which has a significant effect of cost saving,yield increasing and income increasing.Based on the research status of hole forming transplanting technology and equipment,aiming at the problems of large difference between the physical size of hole formed by the existing hole forming device and pot seedling,low soil porosity of hole wall and much soil return in the formed hole,this paper carried out the theoretical research and performance test of hole forming mode,hole shape stability and corresponding equipment,and developed the reverse rotary type soil taking and hole forming device.The main research contents and conclusions are as follows:1.Experimental study on hole forming mode and shape of soil openerIn order to reduce the disturbance of soil caused by hole forming operation of hole opener,based on the working conditions of the vertical soil inserting of the soil opener.Two kinds of hole forming methods,extrusion and soil taking,were selected,by taking the soil return coefficient of section in the hole and soil porosity of hole wall as indexes.Combined with the discrete element method,the operation quality of the hole former under the two hole forming modes is simulated and verified by the soil tank test.The results showed that the soil taking type was a relatively better hole forming method,the soil porosity of the hole wall was 48.5%,more than extrusion,the soil return coefficient of the section in the hole was 0.08.less than extrusion.Based on the soil taking type of hole forming method,different shapes of the soil opener(square cone,cone and rhomboid)were selected for the simulation test of hole forming operation,by taking the soil entry resistance of soil opener and the soil return coefficient of section in the hole as indexes.The relationship between the shape of the hole former and the operation quality of the hole former was studied.The test results showed that the better shape of the soil opener was cone,and the preliminary optimization parameters of the soil opener were: the bottom size was 35 mm,the soil entry depth was 65 mm,the soil entry resistance of the hole forming operation was 62.8 N,and the soil return coefficient of the section in the hole was 0.07.2.Study on the interaction between soil opener and soilAccording to the dynamic analysis of each operation stage of the hole opener,and it was found that the bottom size,soil entry angle and soil entry depth of the soil opener were the main factors affecting the power consumption of the hole forming operation.The static analysis of each operation stage of the hole opener shows that: The adhesion between the outer wall of the soil opener and the soil was positively correlated with the closed soil taking speed of the soil opener,and the soil entry angle was negatively correlated with the adhesion between the outer wall of the soil opener and the soil,the greater the adhesion between the outer wall of the hole former and the soil,the lower the soil stability of the hole wall.The kinematic analysis of soil particles on the cave wall during the each operation stage shows that: In the soil taking stage,only the soil particles on the longitudinal side wall within 0 ～12.1 mm were separated from the hole wall and return to the bottom of the hole under the action of adhesion.During the soil lifting stage,there was no back flow of soil particles on the transverse hole wall,that is,the soil particles on the transverse hole wall have stabilized after the soil borrowing stage.3.Parameter optimization of soil openerIn order to reduce the operation power consumption of the hole opener and the amount of soil returned to the hole during the hole forming operation.The bottom size of soil opener,soil entry angle and soil entry depth were selected as the influencing factors.The multi-objective optimization simulation test was carried out by using response surface method,and the mathematical models of soil return rate of section in the hole and soil entry resistance of soil opener were established.The influence law and optimal parameter combination of the parameters of the soil opener on the quality of hole forming operation were obtained.The optimal results showed that the order of influencing entry resistance was the depth of entry,the angle of entry and the size of the bottom of the soil opener.The order of influencing the soil return rate of the section inside the hole is the angle of entry,the depth of entry and the size of the bottom of the soil opener,the optimal parameter combination of the hole opener is: the bottom size was 39.0 mm,the soil entry angle was 20.5°,the soil entry depth was 60 mm,the minimum soil return rate of the section in the hole was 6.4%,and the soil entry resistance was 64.5 N,the diameter of the formed hole was 83 mm and the effective depth was 45 mm,which met the requirements of pot seedling transplantation.4.Discrete element simulation analysis of hole forming processUsing EDEM software to simulate and analyze the hole forming process,and study the micro mechanism of hole forming and the influence of hole forming speed on the soil stability of hole wall.The results showed that the soil return rates of the section in the hole under the three hole forming speeds were 6.1%,6.3% and 6.4% respectively,and the soil heave degrees of the mouth hole were 4.5%,4.7% and 5.1% respectively.The greater the speed,the greater the disturbance range of the soil particles on the longitudinal hole wall.When the hole forming speeds is 0.25 m/s,0.32 m/s and 0.38 m/s,the displacement of the longitudinal particles on the hole wall first increases and then decreases,while the displacement of the transverse particles on the hole wall and at the bottom of the hole is basically unchanged;with the increase of hole forming speed,the greater the displacement of soil particles on the longitudinal hole wall in the soil taking stage,the displacement of particles on the transverse hole wall and at the bottom of the hole is basically unchanged.In the longitudinal and transverse measurement areas before and after hole forming operation,the closer to the wall of the formed hole,the smaller the soil porosity.Before and after hole forming operation,the change rate of soil porosity in the longitudinal direction of the soil opener was greater than that in the transverse direction,while the porosity at the bottom of the hole basically did not change.When the soil inserting stage of the soil opener was completed,the resistance of the hole forming operation reached the first peak(62.6 N、64.5N、66.7 N).When the soil opener entered the soil taking stage,the force on the soil opener first decreased and then increased.When the resistance reached the second peak at the end of the soil taking stage,the force on the soil opener first decreased and then gradually stabilized in the soil lifting stage.The hole forming speed has little effect on the stress of the hole opener.5.Design of reverse rotary soil taking type hole forming deviceIn order to realize the operation functions of the soil taking type hole opener,such as vertical soil penetration,closed soil borrowing,vertical excavation and so on,a reverse rotary soil taking type hole forming device composed of rotation system,hole forming mechanism,hole forming cam and push rod cam were designed.According to the operation requirements and working sequence of each mechanism in the hole forming process,the structural parameters and position parameters of the annular guide rail and sprocket in the rotation system were designed.6.Soil groove test of hole forming deviceManufacture the prototype of hole forming device for soil groove verification test.It was obtained that the hole mouth diameter,the relative errors of the simulated values of the diameter of formed hole,the effective depth,the entry resistance and the soil return rate of the section inside the hole with the soil groove test results were 4.8%,3.7%,4.9% and 8.8%,respectively.which verify the correctness of the simulation results.The performance test of hole forming device under different soil moisture content was carried out.The test results showed that when the soil moisture content was between 10.2%～ 29.7%,the average qualified rate of formed holes was between 82.0% ～ 96.6%,and the hole formation frequency was between 89.6 and 90.1 hole / min,and the change rates of hole mouth size were 25.6%,9.0% and 7.3% respectively.After the completion of hole forming operation,the average soil heave degree at the mouth of the hole was 0.2%,5.1% and 4.8%respectively,and the soil return rate of the section in the hole was 21.8%,6.4% and 6.2%respectively.The verticality of hole operation under different forward speeds,the test results showed that the minimum angle between the motion track of the soil opener and the horizontal direction was 88°,the hole opener has good verticality in the process of excavation. |
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