Analysis And Experimental Study On The Spreading Uniformity Of Dazomet

In recent years,blight,bacterial wilt,root nematode and other diseases caused by soil-borne pathogens have occurred frequently.Dazomet is soil fumigation agent,and it is increasingly used in soil sterilization.On the basis of consulting a large number of literatures,this paper finds that there are many studies on the pharmacology of dazomet,but few reports on the research on the variable spreading technique and machine of dazomet and most of them are artificial.In order to improve the deficiency of dazomet,the lack of theoretical research on the process of spreading,and there are few studies on the mass and uniformity in the specified area,this paper,using existing spreading apparatus and combining of blocking box from the independent design built spreading apparatus for dazomet,to carry out the dazomet movement analysis and test in the spreading process.Specific research contents are as follows:(1)The paper designs the blocking box by ourselves,and sets up the dazomet spreading device with the existing spreading apparatus and introduces the working principle of the device.Based on the mechanical structure of the device,the movement characteristics of the dazomet particles on the disk and in the blocking box are analyzed,and the motion models of the particles in each process are derived,which provides a theoretical basis for experimental research.At the same time,the method of spreading area with box is also analyzed.The particles in the spreading area is small rectangle,and the spreading area of particles without box is the superposition of two fan surfaces.(2)The speed control unit and opening degree control unit were analyzed and the mathematical model of each unit was established.The simulation dynamic diagram was built in Matlab/Simulink module.In order to reduce the influence of external interference on the process of spreading and improve the stability of the device,the PID control algorithm is designed for each unit.Critical proportion method is used for each unit of the PID controller parameter setting,and determine PID controller parameters of the disk rotational speed unit for K_p=12.35,K_i=1.05,K_D=0.26,and PID controller parameters of the opening degree control unit for K_p=17.64,K_i=1.4,K_D=0.35.Simulation results showed that the designed PID controller can improve the uniformity in the process of spreading.(3)Combined with the theoretical analysis of the spreading process and related literature,the test of the dazomet device was carried out with the working parameters of the disk rotational speed(A),the size of the opening degree(B),and the forward velocity(C)as the control factors,and the mass(M)and uniformity(CV)(coefficient of variation)in the special area as the test indexes.Based on the Box-Behnken test method,a three-factor,three-level combination test was designed and carried out.The mathematical models between the mass,uniformity and working parameter of the disk rotational speed,the size of the opening degree,and the forward velocity are obtained from the measured test data.The results of ANOVA indicate that the mathematical model of mass,uniformity are very significant(P<0.05).The results of ANOVA of the mass showed that A,AB,AC,A~2,C~2 had no significant effect on the mass(P>0.05),and BC,B,C,andB~2 had significant effects on the mass(P<0.05).The results of ANOVA of the uniformity showed AC,B~2,BC had no significant effect on the coefficient of variation(P>0.05),while A,B,C,AB,A~2,C~2 had significant effects on the coefficient of variation(P<0.05).In order to demonstrate the accuracy and rationality of the mathematical model,a verification test was carried out under the conditions of working parameters as rotational speed of 800r/min,opening degree of 60%and velocity of 0.6m/s.The test results show that the average relative error of the mathematical model is 15.11%,which does not meet the technical specifications(the error of the mathematical model is?15%).The average relative error of the uniformity mathematical model is 14.64%,which conforms to the technical specification standard(the uniformity error?40%).In order to explore the influence of the box on the spreading uniformity of dazomet,comparative experiments were carried out under two conditions with and without the box.The results showed that the average coefficient of variation with the box was lower than that without the box,which further indicated that the box could improve the spreading uniformity of dazomet.(4)According to the mathematical model of the mass and the coefficient of variation at the special spreading area,it is found that the minimum coefficient of variation is the optimization objective in the spreading process of the dazomet spreading device based on the prescription map,and there may be multiple working parameter combinations corresponding to the value of the coefficient of variation.In this paper,a control strategy was proposed to obtain the working parameters at the special spreading area,which can provide reference for the subsequent control algorithm.The control strategy is as follows:based on the mass given in the prescription map,the working parameters of the special area are obtained by combining the mathematical model of the mass and coefficient of variation.In order to further validate the accuracy and rationality of control strategy,application test was conducted,and the mass of three spreading area seems the average relative error is less than 15%,coefficient of variation were less than 40%,that shows working parameters combination based on the control strategy can satisfy the dazomet spreading technical requirements.