| China is a traditional agricultural country,and the agricultural field has always been a key development and research direction in China.The comprehensive control of crops is a key link in agricultural development.However,China’s pesticide spraying technology is outdated and the utilization rate of pesticides is low,which has a serious impact on the development of China’s agricultural economy.Variable spray technology can effectively improve the pesticide utilization rate.This paper aims at the problem of low pesticide utilization rate caused by uneven distribution of pesticide droplets in the process of spray operation in the quantitative application mode of conventional field spray equipment.In this paper,the overall structure of the spray system,the software and hardware of the control system and the control algorithm are studied,and a variable spray system that can change the flow rate with the change of spray machine operating speed was designed.The system uses multi-sensor real-time monitoring system for flow,pressure,operating speed,liquid level and other information,and takes this as the control basis.It uses the self-learning ability of BP neural network to modify the PID control parameters in real time,accurately adjust the spray flow,so as to improve the pesticide utilization rate.The main research content of this article is as follows:(1)Based on the analysis of the current situation of variable spray systems at home and abroad,a variable spray system that changes the flow according to the operating speed of spray equipment is proposed,and the overall design of the system is completed.According to the overall design scheme,the nozzle,diaphragm pump,high-speed switch solenoid valve,pressure sensor,flow sensor,speed sensor and other components were selected,and then the variable spray system was constructed.The liquid flow resistance loss and local water flow loss of spray system pipeline are calculated quantitatively and pressure compensation is carried out.(2)The mathematical model of the controlled system was established,and the PID compound controller and traditional PID controller based on BP neural network were designed.The traditional PID controller and BP neural network PID controller were simulated and analyzed under the Simulink platform.The simulation results showed that the BP neural network PID control was superior to the traditional PID control in overshoot,steady-state error,rise time and adjustment time.(3)The software and hardware design of variable spray system was completed.STC12C5A60S2 single chip microcomputer is selected as the MCU of the control system,and the hardware circuits of the power module,sensor module,actuator module and communication module of the control system are analyzed and designed.In the software part,Keil software is used to complete the programming of each module of the variable spray system,and the GUI module of MATLAB software is used to complete the design of the upper computer of the spray system.(4)Experimental research was carried out on the spray integrated platform.Using the spray performance comprehensive platform,the spray angle,droplet size and spray uniformity of the nozzles used in the system were tested and studied under spray pressures of 0.2 MPa,0.25 MPa,0.30 MPa,0.35 MPa,0.40 MPa,0.45 MPa and 0.50MPa,respectively.The test results show that when the spray pressure of VP110-10nozzle is 0.40 MPa,the spray effect is the best.At this time,the spray angle is about110°,and the droplet size is 77.665 um(less than 100 um).At this time,the variation coefficient of each nozzle flow is small,which meets the quality requirements of spray operation;When the spray pressure is 0.40 MPa and the solenoid valve frequency is set to 10 Hz,the duty cycle adjustment range of the control signal is 30%～80%;According to the measured data,the 8 nozzles of the variable spray system are reasonably arranged on the spray boom.(5)The field experiment of variable spray was carried out with broad bean plant as the object of spray.By setting the flow control accuracy of the measurement system under the conditions of different dosage and operating speed of the spray truck,use water sensitive paper to detect the number of droplets deposited on each layer of the plant,and set the operating speed of the spray truck to 0～2.5 m/s to test the following effect of flow and speed.The results show that the variable spray system can adjust the spray flow adaptively according to the operating speed of the spray truck.The maximum flow deviation is 2.17%when the spray truck operates at constant speed,and 3.4%when it operates at variable speed;The scanning result of water sensitive paper shows that the minimum droplet deposition density is 33 particles/cm~2,which meets the requirement of no less than 30(particles/cm~2)in GB/T 17997-2008 Pesticide spray Field Operation Procedures and Spraying Quality Assessment,and the variation coefficient of droplet deposition quantity is 6.02%,far less than the national standard;The following results of flow and speed show that the average deviation between actual flow and theoretical flow is 5.88%,which has a good following effect. |
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