Study On Variable Rate Fertilization Control System Of Pnuematic Topdression Machine For Paddy Field

Abstract:In the traditional farming process,the fertilization method is mainly based on manual fertilization or pure mechanical fertilization,and the efficiency of manual fertilization is not high,and it is more dependent on the cultivation experience of farmers.Compared with manual fertilization,pure mechanical fertilization improves fertilization efficiency,but the control of the amount of fertilizer is not fine enough,it is likely to cause the error of the quality of fertilizer.With the occurrence of precision agriculture and the development of science and technology,variable ratio fertilization technology as an important component of precision agriculture is an effective means to solve the above problems,and variable ratio fertilization control system is the key of variable fertilization technology.At present,most of the domestic researches on the variable ratio fertilization control system are focused on the variable ratio fertilization control of the dry farmland,and the researches on the variable ratio fertilization control for paddy field are less,and the researches on the pneumatic fertilization machine are also lacking.In the south of china,rice is the main food crop,and in the whole growth stage of rice,it is often necessary to carry out top dressing operations according to the growth situation of rice,which has important influence on the rice yield and fertilizer utilization rate.In view of the above problems,this paper designs a variable ratio fertilization control system based on the pneumatic topdressing machine for paddy field.The system is used in conjunction with the high ground-clearance tractor,which is mainly applied to variable ratio topdressing for paddy field.Through the comparative analysis of control system drive scheme,speed measurement scheme and control scheme,the overall scheme of variable ratio fertilization control system is determined.The overall scheme mainly includes the DC motor drive scheme applied to the small and medium-sized fertilization machine,the speed measurement scheme based on GPS and the closed-loop control scheme beased on PID algorithm.At the same time,the relationship between the motor speed and the amount of fertilizer applied per minute is calibrated.In order to obtain better control effect,the mathematical model of the DC motor and the motor drive unit is established,and the transfer function of the system control link is obtained.By measuring the actual step response curve of the system,the parameters in the first-order transfer function are determined.By the Matlab/simulink simulation,the comparation between the first-order model and the second-order model is made.The PID control algorithm is used to realize the closed-loop control of the system,and the ideal PID parameters are set,in which the K_p,K_i and K_d are 0.47,0.023 and 0.021 respectively.After a series of theoretical analysis,the control system is divided into upper android device and lower computer controller,and the two parts are designed respectively.The lower computer controller mainly includes the system power supply circuit,the STM32control circuit,the motor drive circuit,the serial communication circuit,the WiFi communication circuit,the sensor circuit,the communication protocol and control program.Based on the upper Android decive,the variable ratio fertilization control software is developed,and the corresponding user interfaces are presented.Finally,the variable ratio fertilization control system is tested.It mainly includes the system function test,the system speed following characteristic test,synchronizing constant speed fertilization,synchronizing variable speed fertilization and width direction variable rate fertilization.The results of the system function test show that the functions of the control system can run normally,and that the communication between the upper android device and the lower computer controller is well,and that the whole system can carry out the normal fertilization operation.The speed-following characteristic test shows that when the target speed changes,the actual speed follows the target speed rapidly,and that the maximum relative error of the rotational speed is 2.55%,the minimum relative error is0.35%,the maximum standard deviation is 1.44r/min,and the minimum standard deviation is 0.81r/min.It also proves that the variable ratio fertilization control system designed in this paper has better speed follow performance,and that the discrete degree of actual revolving speed is low,and that the error between actual revolving speed and target revolving speed is in acceptable range;The synchronizing constant speed fertilization test shows that the maximum standard deviations of the two kinds of fertilizers are 20.71g and13.66g respectively,which indicates that the speed synchronism of the four fertilizing motor is higher,and the uniformity of fertilization is ensured;The synchronizing variable speed fertilization test shows that the errors of two kinds of fertilizers are lower than 5%under the effect of control system;The width direction variable rate fertilization test shows that the ferlitization error of single side is still lower than 5%.Of course,there are still many factors that affect the effect of variable ratio fertilization,this paper mainly build a pneumatic variable ratio fertilization(topdressing)platform for paddy field and laid the foundation for further research.