| As a kind of green,environmentally friendly harvesting increasing technology with high output and high efficiency,vegetable grafting and seedling cultivation can effectively overcome continuous cropping obstacles and diseases,which are caused by successive years of planting,as well as insect pests,and reduce application of pesticides and fertilizers.For the tiny and tender vegetable seedlings and their individual variation,artificial grafting is not efficient and cannot ensure its working quality;while mechanized grafting can realize standardized producti on of grafted seedlings.Grafting machine is the core equipment for grafting and seedling cultivation in industrial production,and can efficiently alleviate seedling cultivation factories’ reliance on manpower,replace manual grafting and can improve grafting quality and production efficiency.For the poor adaptability of current grafting machine on seedlings,seedling damage and low cutting precision,it is necessary to conduct in-depth researches on mechanized grafting technologies,such as flexible clamping on seedlings and precision cutting mechanism.Taking melon(watermelon and cucumber)seedlings as the research object,realizing flexible clamping and precision cutting as research target,a theoretical analysis and in-depth study was made on the key steps of grafting,such as flexible rootstock feeding and locating,seedling cutting mechanism,flexible clamping and delivering,mechanical properties of the grafting clip and automatic clamping,by combining mechanized grafting technologies,simulation a nalysis and bench test.The study is aimed at providing theoretical basis and technological reference for development and optimization of mechanized grafting equipment for melon crops.The main research contents are as follows:(1)Measurement of the parameters of melon grafting seedlingsAfter analyzing the mechanized grafting methods for melon vegetables and parameter measuring,the characteristic parameters of rootstock cotyledon,seedling stem,pith cavity and growing point,the geometric parameters of cotyledons and seedling stems of scion,bearing capacity of rootstock cotyledon and compression characteristics and shearing characteristics of seedling stems were obtained to lay a theoretical basis for design of the actuator of the grafting device.(2)Study on airflow field of flexible seedling feeding and locating mechanism for rootstocks based on the software CFDBy adopting a working method of combining positive pressure air blow and negative pressure adsorption,the author did profiling design of the working plane of the absorbing and air blowing module by obtaining the curve of reverse side of cotyledons and developed a flexible seedling feeding and locating mechanism for rootstocks.The CFD software was used to simulate the negative pressure airflow field of the adsorption module.It was obtained that the vacuum negative pressure was 3 k Pa,suction hole diameter was 1 mm,the hole depth was 4 mm.The average pressure of suction hole was 972.38 Pa,which was lower than the yield pressure at breaking point of white seed pumpkin and bottle gourd.Numerical simulation was made on the positive pressure airflow field of air blow module.Under conditions of inlet velocity of 30 m/s,air blowing distance of 30 mm,the average air flow velocity of cotyledon working plane was 1.816 m/s,satisfying the technological requirement of seedling pressing by air blow.The seedling feeding and locating test of rootstock cotyledons showed that,the success rate of seedling pressing by rootstock cotyledons reached 98.67%,adsorption rate reached 98.33%,and there was no cases of seedling damage.The test results showed that,profiling design of flexible seedling pressing and locating through positive and negative air flow was reasonable and provided reference for the flex ible seedling feeding and locating of rootstocks.(3)Analysis and test study on seedling cutting mechanism and parametersIn order to clarify the working area for cutting rootstocks,an experimental analysis on the interior structure of pith cavity and growing point of rootstocks were made,and the cutting angle for matching rootstocks and scions were determined,then a kind of tilted cut-pasted grafting method was proposed to improve the docking precision between rootstocks and scions.A rotary cutting device for growing points of rootstocks was designed,and the position relationship between center of rotary cutting and center of section plane was determined through theoretical study.The cutting mechanism of the scion and seedlings was developed,and th e multi-layered V-shaped seedlings were designed.The force analysis on seedling pulling process showed that,the angle of the V-shaped outlet of the seedling block was determined as 90°,and the parameters in scion cutting were optimized.The performance test results of cutting mechanism showed that the success rate of scion was 99.33%,success rate of cutting was 100%,and cutting accuracy was 97.75%,which indicated that the structural design of the V-shaped structure was reasonable and had good effect on scion stems of matching seedlings.The success rate of rootstock pressing was 96.67%,success rate in cutting was 98%,and the cutting accuracy was 96.8%.It shows that it is feasible to change the angle of the cutting plane by adjusting coordinates of t he rotary cutting center.The joint rate between rootstocks and scions was 98.53%,and the working precision satisfied requirements in grafting.(4)Kinetic analysis on flexible clamping and delivering mechanismA flexible clamping method based on cushioning material was proposed and a flexible clamping gripper was designed.By adjusting the clamping distance of the crash pad,precise control of the clamping force on seedlings was realized.The compression mechanical properties of the EVA cushions with a thickness of 3 mm and 5 mm showed that when the clamping distance of the crush pad was 0 mm,the cushion with thickness of 3 mm had a risk of damaging white seed pumpkin and bottle gourd seedlings,while the cushion with thickness of 5 mm cushion could clamp the seedlings of white seed pumpkin,bottle gourd,cucumber and watermelon stably.A four-gripper rotary delivering mechanism was designed,with rotary positioning accuracy 0.03°and theoretical production efficiency 1107 seedlings/h.After dynamic simula tion on the clamping and delivering mechanism based on ADAMS,the relationship between different clamping force and displacement of seedlings was analyzed.Simulation results showed that,when rotating speed of the delivering mechanism was 1 r/s and the clamping force was below 0.4 N,the seedlings would get away from the gripper;when the clamping force reached 3.5N,there was no seedling displacement.(5)Mechanical properties of the grafting clip and test study on the clamping mechanismThrough constructing an analysis model between the clamping force of grafting clamp and displacement of steel ring mouth by applying the software ABUQUS,an automatic clamping device was designed to realize precise clip discharge and clogging prevention.When inclination angle of clip slideway discharging was 50°,pressure of pushing air cylinder was 0.4 Mpa,the success rate of clip setting reached 98.67%,which could satisfy the technological requirements in mechanized grafting.The force conditions of stretching and compression on the clamp were analyzed,and tests on mechanical properties of the grafting clamp showed that,the clamping force model of the grafting clamp was reasonable and could express the clamping characteristics of the grafting clamp.The grafting clamps with steel wire diameter of 0.7 mm are safe and reliable to cucumber and watermelon grafted seedling,while the clamping force of grafting clamps with steel wire diameter of 0.8 mm is larger than the safe pressure on cucumber grafted seedlings,causing risks to the clamping of cucumber grafted seedlings.The critical thrust in clip setting was 1.59 N,which provides reference to the successful setting of grafting clips.(6)Overall design and test study on the cut-pasted grafting device for melon cropsIn this study,the technological requirements and key problems in the design of cut-pasted grafting mechanism for melon crops were proposed,the flow chart of the grafting mechanism was drawn,the overall scheme design and function layout were completed,t he working process and parameters of the grafting mechanism were discussed,to design the sample machine for the cut-pasted grafting device for melon crops.Taking grafting of cucumber and white seed pumpkin seedlings as an example,the success rate of actuators were studied from the aspects of seedling feeding,cutting and automatic clip setting,test results showed that,grafting production rate reached 1054 seedlings/h with grafting success rate of 91.65%. |
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