| Precision agriculture is the development trend of future agriculture.The development trend of China’s agriculture is from traditional agriculture to precision agriculture.Variable spray technology is an important part of precision agriculture.It is the most closely related part of precision agriculture with food safety and environmental pollution.Variable spray mixing methods include premixing pesticide and online mixing pesticide.At present,the domestic variable spray mixing method is mainly premixing.The spray amount change can be realized by changing the application amount when the concentration of the pesticide is constant.It is not possible to change the concentration of the pesticide according to the degree of pests and diseases of different plots.The operator needs to be in contact with the pesticide,which is harmful to the operator.It has the disadvantages of large amount of pesticides and environmental pollution.Online mixing pesticide technology can solve the shortcomings of premixing pesticide.It can complete the online mixing of pesticide and water solvent by setting the medicine box and water tank separately.The online pesticide mixing technology achieves on-demand dispensing and precise pesticide application,which has the advantages of ensuring accurate use of pesticides,avoiding pesticide waste,avoiding operator contact with pesticides and improving the ecological environment.In this thesis,in order to solve the problems existing in the existing plant-mixing machinery online mixing device.In order to reduce the transmission time delay of the online mixing pesticide system and ensure the uniformity of the pesticide mixing,the injection-type online mixing pesticide spraying system designed for variable spray and width control is adopted.The outlet end of the spray pump is divided into multiple ways to inject the liquid medicine,and the SK static mixer is installed to enhance the uniformity of the mixing pesticide.The start and stop of the independent grouping solenoid valve is controlled to realize the operation width control.During the spraying operation,the online mixing pesticide spray system adjusts the water solvent flow rate and the liquid pesticide flow rate in the current sprayer system circuit according to the mixing ratio provided by the user setting or the prescription chart,and controls the concentration at the nozzle to realize the variable of the spray operation.The specific research work is as follows:(1)Design of online mixing pesticide device.Firstly,three kinds of control methods for changing the amount of spray were analyzed,and an injecting online mixing device based on the adjustment of the amount of liquid injection was designed.The device includes a water solvent adjustment system and a liquid injection system.Secondly,the two adjustment methods of the water solvent adjustment system are analyzed and compared to determine the bypass flow to adjust the water flow.(2)Research and development of online mixing pesticide control system.The control system hardware and software are designed.The controller is designed based on STM32F4 chip,including the minimum system unit,signal acquisition unit,power conversion unit and execution drive unit.It can complete data acquisition and processing such as flow pressure,metering pump and solenoid valve.And electric control valve drive.The control system includes two modes of operation,automatic and manual.The upper machine is designed for water solvent flow and liquid flow setting and real-time display of water solvent flow and instantaneous flow rate.(3)Online compound control system test.In this thesis,the water solvent flow rate is adjusted by controlling the opening degree of the electric control valve,and the highprecision chemical liquid flow real-time detection technology and the DMC dynamic matrix control algorithm are used to realize the detection and control of the liquid injection amount.A series of tests such as spray mixing ratio range determination,realtime dynamic response test and steady-state error test,uniformity of pesticide mixing test,etc.The mixing ratio range measurement test shows that the mixing ratio adjustment range is 12:1-150:1.The dynamic response test and the steady-state error test showth that the steady state characteristics of the water solvent flow are good.The average steadystate error of the system liquid injection in the DMC dynamic matrix control does not exceed 5%.The system performs the mixture uniformity under different mixing ratios and the spatial variability of the detection was less than 5%.It is indicating that the mixing pesticide system has better mixing performance. |
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