| Variable rate spraying technology had become a direction for the development of modern agriculture,online pesticide mixing as one of the variable rate spraying technology,developed rapidly because of its' saving in pesticide,safe and reliable process for mixing and so on.However,there are still some problems such as the low mixing ratio and narrowed range of adjustable raotio.The mixed ratio of the online mixing system is much related to the mode of mixture and the method of controlling the flow of pesticide in the process of mixing.The jet mixing device is widely used for online mixing system because of its' simple structure and low cost,while the pulse width modulation(PWM)control technology can solve the problem of controlling of the pesticide flow control inhaled by the jet mixing device with fixed structure parameters,so as to solving the problem of adjustment for mixing ratio(mixed ratio: ratio of water to pesticide).In this paper,online jet mixing system was built for jet mixing device.The flow control system based on PWM was designed,and the mixing effect of online jet mixing system while the PWM control technology was used to control the flow of system was studied.It was desirable to control the flow of pesticide by the PWM technology to achieve the purpose of controlling the mixing ratio of the online jet mixing system.The research work carried out in this paper mainly includes the following aspects:1.Build an online jet mixing system According to the analysis of domestic and foreign methods of online mixing and actual needs of the subject.The online jet mixing system mainly included the three-cylinder plunger pump,flow meters and pressure gauge were built.The parameter of each component is determined according to the actual mixing demand.And the model is selected to meet the requirements of the mixing system.2.Determine the parameters of the jet mixing devices According to the requirements of the online mixing system,jet mixing devices with different area ratios was designed.According to the requirement of the actual spray needs,Combined with three types of agricultural spray nozzle,The experimental were carried out on the mixing performance of the jet mixing device with different area ratio in different spray systems.A jet mixing device with better performance and stable working conditions were selected for subsequent pesticide mixing control tests.3.Design,simulation and test of pesticide flow control system From the principle of PWM control flow,combined with needs to adjust the PWM frequency and duty cycle in the process of actual use to determine the hardware design.Through the analysis of the principle of PWM signal generation,the software program design of the control system is determined.On this basis,the liquid flow control system is set up,and the performance of the flow control system was tested,which proves that the system can realize the flow control.4.Experiment of mixing ratio of online jet mixing system For the whole online mixing system,the mixing ratio of different PWM signal and duty ratio was tested under the spray pressure of 0.3MPa.According to the test results,the mathematical model of mixed ratio control was established and imported into the control system.The mixing test was carried out,and the uniformity of the system mixture was measured.As a result,the relative error of the system mixing ratio is less than 10.5% when the different mixing ratio is set,and the mixing ratio is adjustable in the range of 11: 1 ~ 150: 1.The coefficient of variation of the concentration of the mixed liquid was less than 10% under different mixing conditions,and the uniformity of the system was good.It is proved that the combination of flow control system and jet mixing can improve the mixing ratio of online mixing system,expand the adjustment range of the mixing ratio,and the effect of the mixture is good,and it is confirmed that the system has certain popularization value. |
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