| Rice,as one of the main grain crops in China,has the characteristics of “grain crop-cash crop-forage rotation” structure,which occupies an extremely important role in grain crops.With the development of scale and industrialization of ri ce cultivation in China,on the premise of ensuring relatively balanced cultivated area of rice,decreasing the large amount of input of agricultural factors of production to reduce agricultural non-point source pollution,promoting the green development of rice industry has become the primary task of rice production safety.Electrostatic spray technology can use different charging methods to bring polar charges to the liquid droplets of the medicine and generate electrostatic fields between the droplets an d the target of the spray at the same time.Then under the combined action of electrostatic field force and other external forces,directional motion is carried out and the droplets are adsorbed on each part of the target,and the plant protection work is completed efficiently and uniformly.This technology has the advantages of increasing the hit rate of spraying to target,reducing the use of pesticide,increasing the coverage rate of droplets and has good adhesion effect to different parts of plant leaves,which matches the national strategy of green agriculture development in China.It has great significance for improving the utilization rate of chemical pesticides,increasing the yield and quality of crops and reducing agricultural non-point source pollution.Boom sprayer is the most widely used plant protection machine.The development of boom sprayer to high power,high ground gap and wide spraying amplitude has a positive effect on improving the application efficiency and reducing the damage to crops i n the process of operation.The traditional boom sprayer adopts mechanical spray rod structure,and its folding and unfolding is accomplished by several hydraulic cylinders.There are some problems,such as poor synchronization,coordination and operation,high manufacturing cost and low reliability of the machine and tools,etc.In the process of field spraying and road surface transferring,the external excitation caused by road surface fluctuation will result in vibration of the sprinkler rod,especially under the condition which the ground is close to the natural frequency of the spray rod,the frequency of the spray rod will be coupled with the external excitation frequency,which seriously affects the spray quality.To counter the problems mentioned ab ove,combined with the planting mode of paddy field and the requirement of plant protection agriculture,and considering the factors such as working efficiency,uniformity and universal applicability of pesticide application,this thesis,by consulting domestic and foreign references,theoretical analysis,computer virtual optimization design and so on,combined with finite element simulation analysis,modal and field performance test,carrying out the design and experimental study of electrostatic spraying device for paddy field sprayer in order to solve the practical problems existing in the operation of paddy field plant protection.This study provides a reference for simplified design of spray device and rational configuration of electrostatic spray system for paddy field sprayer.The main contents of the study are as follows:(1)Design of electrostatic spray device for paddy field sprayerAccording to the analytical method,the length of each part of the multi-fold mechanism is determined.On this basis,the thickness of the steel pipe is taken as the influencing factor,and the quality and the first order natural frequency are taken as the test indexes.The mathematical model between factors and indexes is established by using the method of virtual orthogonal test design,optimum design of the wall thickness of different steel pipes is carried out.According to the results of the virtual test,the primary and secondary factors affecting the quality and the first order natural frequency and the optimal level combination are considered.When the wall thickness of circular steel pipe,rectangular steel pipe and square steel pipe are 2 mm,2 mm and 2 mm respectively,the mass of spray rod multi-fold mechanism is the smallest and the dynamic characteristic is the best.The mass is 62.85 kg and the first-order natural frequency is 14.84 Hz.The working principle of induction electrostatic spray head is described,and the selection and configuration of electrostatic spray system are rationally carried out.(2)Modal analysis and test of spray rod multi-fold mechanismTaking the designed multi-folding mechanism of the spray rod as the research object,the finite element model of the spray rod is established by using ANSYS Workbench software,and modal analysis is carried out under the free state(that is,releasing all degrees of freedom).In order to further verify the rationality of the finite element modal simulation analysis,the multi-input multi-output method is used to carry out the modal test of the hammer ex citation.The comparison between the modal test and the simulation analysis results shows that these two methods are relatively similar to each other.The maximum error is 7.14%,and all the matrix forms are basically the same.The reliability of the numer ical model is verified.(3)Performance test and experimental study of electrostatic spray deviceThe performance of the designed electrostatic spray device is tested to ensure that it has good sealing,pressure regulation and unloading performance,anti-drop performance and spray uniformity of the nozzle and spray uniformity along the direction of the spray rod.The results show that the coefficient of variation of spray uniformity in electrostatic spray device and along the spray rod decreases first and then increases with the increase of system spray pressure,and when the spray pressure of the system is 0.3MPa,the coefficient of variation of uniformity of spray volume of electrostatic spray device is 2.55%,and the coefficient of variation of uniformity of spray quantity along the spray rod is 13.61%.The test results of sealing performance,pressure regulation and unloading performance and spray head drop prevention performance all meet the national standards.(4)Configuration and field test for paddy field sprayerIn order to further explore the influence of the main working parameters of paddy field electrostatic spray device on its deposition uniformity,and to verify the quality and reliability of the electrostatic spray device designed in the field,a multifunctional power chassis with high clearance and folded waist was used as the carrier.And the chassis carried with the electrostatic spray device designed in this paper is equipped with a sprayer used in paddy field,to carry out its field performance test.The spray pressure of the system,the advance speed of the machine and the height of the ejector rod are selected as the test factors,and the coefficient of variation of the coverage rate is used as the evaluation index.The field performance optimization experiment is carried out,and the mathematical model between the deposition uniformity index and the test parameters is established.Design-Expert 8.0.6 software was used to optimize the test results,and the optimal working parameters were obtained.The experimental results show that when the spray pressure of the system is 0.7 MPa,the forward speed of the machine is 5.56km/h and the height of the ejector rod is 697.51 mm,the coefficient of variation of the electrostatic spray device coverag e is the lowest,that is,the uniform performance of droplet deposition in the device is the best.The coefficient of variation of coverage was 21.53%. |
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