Research And Development Of Multi-stage Temperature Control System For Extruder Based On PFC-PID Coupling

Extruder is the main equipment for producing plastic products,and its temperature control system has the characteristics of strong correlation,non-linearity,large lag and so on.Therefore,the temperature control system often has a large error value in production.However,errors in the temperature control system have a serious impact on plastic production.First of all,the difference of temperature will affect the reaction and mixing of the materials.Since the material particles are very sensitive to the reaction temperature,temperature fluctuations will increase the scrap rate of the product.Furthermore,the temperature difference will also affect the performance of the extruder.Due to uneven temperature,a small amount of plastic may solidify in the barrel,resulting in extended maintenance time and increased maintenance frequency of the extruder,affecting normal production operations.Finally,the detection has a lag.Because the detection link in the pipeline lags behind the extruder by 1 hour,the unqualified product generated when the problem is found has hundreds of kilograms,which seriously increases the operating cost of the enterprise.In response to the above problems,it is necessary to seek a parameter-adapted extruder temperature controller,which can not only adapt to the complex working conditions of the extruder,but also reduce the influence of many influencing factors on the temperature control,so as to achieve a high performance in the temperature range index.This article will design an adaptive proportional-integral-derivative control(PID)controller based on predictive function control(PFC),using PFC-PID coupling for control,and a good control effect is obtained.The main content of this paper is as follows:(1)Introduced the structure of the extruder and the plastic extrusion process,focused on the control process of the temperature control system of the extruder,and analyzed the existing problems of the temperature control system,and pointed out the solution and direction.(2)For temperature control,a large time-delay system,model predictive control is applied to temperature control,coupled with PID control,and model predictive control is used to set parameters for PID.At the same time,based on the actual situation of the temperature control of the extruder,the temperature control of the extruder is divided into two stages of heating and heat preservation,and the PFC model and the MPFC(multivariable PFC)control model are established according to the actual situation.Finally,the related control parameters of PFC are tuned according to the existing rules.(3)To solve the problem that the temperature field coefficient is relatively complex and the heat transfer coefficient is difficult to measure,the method of time series analysis is used.Firstly,the combination of statistical hypothesis testing and model fitting test is used to determine the model structure.The model parameters are estimated by recursively increasing the least squares,and the factory production data is extracted.After pretreatment,MATLAB is used to calculate the heat transfer coefficient.(4)Use MATLAB to simulate the PFC-PID coupled temperature control in the heating phase and the MPFC-PID coupled temperature control simulation in the heat preservation phase,thus confirming the effectiveness of the control method.The temperature control results show that the PID adaptive controller based on PFC is more suitable for temperature control than the fixed value controller.(5)Build a hardware experiment platform for the temperature control system supporting the PFC-PID algorithm,use PLC as the bottom controller to complete the PID part control,and use the computer as the upper controller to complete the PFC part control.