Research On Two-stage Jet On-line Mixing System Based On BP-PID Control

Drug application is an important means to ensure the healthy growth of crops.However,the traditional method of pre-mixed drug application threatens the safety of mixed drug users,and it is easy to cause waste of remaining drugs,pollute the environment,and cannot adjust the concentration of drug solution in real time.Online mixing technology can solve these problems.However,the current online mixing technology has the problems of poor mixing uniformity and poor mixing control effect.Therefore,this study uses two-stage jet online mixing technology and BP-PID control technology to carry out the research of two-stage jet online mixing system based on optimized BP-PID control.In this study,CFD technology was used to analyze the influence of mixer structure parameters on the mixing effect,and the structure parameters of two-stage jet mixer were optimized.The transfer function of diaphragm pump and peristaltic pump in online mixing system was established by using optimized BP-PID algorithm,and the control model was constructed and simulated by Simulink.A two-stage jet mixing system based on BP-PID control is designed,and the online mixing control effect of the two-stage jet mixing system based on optimized BP-PID control is investigated through experiments.The main research contents and conclusions are as follows:（1）Structure design and parameter optimization of two-stage jet mixer.The Fluent software was used to simulate the two-stage jet mixer,and the main structure parameters of the main and auxiliary mixer were optimized.The effects of diffusion angle and nozzle-to-tube distance on the mixing effect were analyzed by orthogonal experiment simulation.The model of mixer parameters and mixing efficiency was established by response surface method.The optimal structure parameters of the two-stage jet mixer were obtained as follows:the diffusion angle of the main mixerα₁=10°,the nozzle-to-tube distance d₁=2.6mm,the diffusion angle of the auxiliary mixerα₂=10°,,and the nozzle-to-tube distance d₂=1.3mm.（2）BP-PID control model is established and simulated.The optimal BP-PID control algorithm is used to complete the S function.The input voltage and output flow transfer functions of diaphragm pump and peristaltic pump are established respectively,and the control simulation model is built.Simulink was used to simulate and analyze the response of ordinary PID,traditional BP-PID and optimized BP-PID control algorithms under step function.The results show that with the peristaltic pump as the controlled object,the optimized BP-PID control algorithm reduces the steady-state time by 0.033 s compared with the ordinary PID.Compared with the traditional BP-PID,it not only has no overshoot,but also reduces the steady-state time by 0.013 s.The optimized control algorithm has good control effect on diaphragm pump and peristaltic pump.（3）A two-stage jet mixing system based on optimized BP-PID control is built.According to the requirements of the project,the selection of diaphragm pump,peristaltic pump,main control chip,flowmeter and other main components and the design of power supply,signal acquisition,drive and other related hardware circuit are completed.The lower computer software modules such as input capture,mixing ratio control and BP-PID control algorithm are designed,and the upper computer program is developed by using LABVIEW.（4）Experiment on mixing effect of two-stage jet mixing system based on optimized bp-pid control.The optimized bp-pid,PID and PWM algorithms are used to control the flow of diaphragm pump and peristaltic pump respectively to carry out the experiment of mixing ratio error,mixing uniformity and mixing stability.The results show that the relative error of optimized bp-pid control is the smallest,which is 3.51%;The optimized bp-pid control has the best mixing uniformity,and the average variation coefficient of mixing concentration is 2.78%.Under the same control method,the flow rate of diaphragm pump is 15l/min,and the time variation coefficient of mixed drug concentration is the smallest;When the flow rate of diaphragm pump is 15l/min,the optimized bp-pid control system has the best mixing stability,and the time variation coefficient of mixing concentration is 1.25%.