| Two-stage pusher centrifuge(called centrifuge in short)is a filter centrifuge with continuous operation,large production capacity,less crystallization damage and low moisture content of filter cake.In recent years,it is one of the key equipment of the dehydration and drying process in the salt producing and alkali making industries,which has a vital influence on the separation efficiency and separation effect of materials.In response to the actual needs of the development of the salt and soda industry,with the aim of improving the stability and efficiency of the centrifuge control system,the centrifuge control system was designed by combining the structure and process flow of the centrifuge and the fuzzy PID control technology,which indicates important practical significance,application value and economic benefits.The main work includes the following four aspects.Firstly,the influence of the hydraulic oil temperature on the operation of the centrifuge is investigated.Based on the analysis of the centrifuge system in detail,such as,its overall structure,its working rationale,and the interrelationship among the mechanical,the hydraulic and the electrical components,the conclusion that the temperature is too high or too low is not good for the stability of the control system can be drawn.Secondly,a oil temperature control algorithm of fuzzy PID-based hydraulic is designed.The hydraulic oil temperature control for the current centrifuge adopts a fixed opening cold water valve and there is a problem that the hydraulic oil temperature is too high or too low,resulting the centrifuge to shut down.Applying fuzzy control theory,the hydraulic tank is taken as the controlled object,the transfer function is established by the response curve method,the fuzzy PID algorithm is designed and the Simulink simulation model is established in MATLAB.In comparison with the classic PID control algorithm and the fuzzy control algorithm commonly used in temperature control system,it can be found that the classic PID control oscillates and the overshoot is about 26% as the target temperature is 50°C(the perfect number),the overshoot of the fuzzy control is zero and the steady-state error is about 9%,while the fuzzy PID control has good dynamic and static characteristics such as zero overshoot,zero stability error,and no oscillation.Therefore,the method of fuzzy PID control is used to stabilize the temperature of the hydraulic oil,which can be availably to improve the stability and work efficiency of the control system.Thirdly,a hardware control system based on PLC model is designed.Based on the working environment of the centrifuge,the hardware system was selected.The advantages and disadvantages of three current major control systems,such as,DCS control system,PLC control system and FCS control system are analyzed.Combined the actual conditions and project cost with other factors,the Siemens S7-200 series CPU is regarded as the controller of the entire system.Meanwhile,the distribution of system I/O ports is completed and the peripheral circuits are designed.Fourthly,according to the features and working process of the centrifuge,the model,domain range,and membership function of the fuzzy control algorithm are determined.Meanwhile,the fuzzy PID control rule tables are completed and the fuzzy PID controller based on PLC hardware control system is designed.And then programming language on the software system is written down.Furthermore,the ladder diagram language is used to design and implement the software system in STEP7-Micro/WIN32 environment and the control system logic program is simulated as well.The results indicate that the program design meets its requirement. |
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