Study On The Intelligent Quality Control Technology In Dilution Headbox Of Modern Paper Machine

Intelligent dilution hydraulic headbox,the key technology and equipment for intelligent quality control of modern paper machine is the advanced and energy-efficient at present.It is equipped with an integrated intelligent dilution control system and directly impact on paper quality.This paper is terminated according to science and technology project "Development of domestic high-speed paper machine: Research and development of dilution hydraulic headbox".The work aims to develop intelligent dilution hydraulic headbox of high-speed paper machine with speed of 1200-1400 m/min.Deviation of cross-directional(CD)basis weight needs to reach advanced international level.Focusing on the intelligent quality control technology of the dilution headbox,numerical simulation and experimental research were performed to analyze mechanism of dilution control,intelligent dilution control system,model identification,CD controller and the key components in this study.Moreover,the above research contents ware help to develop and produce the intelligent dilution hydraulic headbox.The main contents of this paper are as follows:Firstly,according to the characteristics of modern high-speed headbox and the requirements of pulp fiber dispersion and flow state,the structure features and CD control system of headbox produced by international famous enterprises were summarized.Furthermore,the characteristics of the main components of the headbox including pulp distributor,turbulence generator and dilution water device were analyzed and compared.For the problems of CD control processes,we analyzed the data measurement,data preprocessing,CD control algorithm,actuator and model identification of the CD control system.The intelligent quality control technology based on the dilution control system was an important research direction of modern high-speed paper machine.Secondly,mainly study the effect of dilution water added to the mainstream on concentration and flow,using the computational fluid dynamics method to carry out the numerical simulation by analyzing the dilution mechanism of adjusting CD basis weight and calculating model of the dilution hydraulic headbox.The variation and distribution of concentration were analyzed by dilution step response method.The results showed that CD concentration distribution was in positive normal distribution,the dilution influence width decreased as increasing the working speed.A dilution response model simultaneously established to provide a theoretical basis for intelligent CD control.Thirdly,for the requirements of the intelligent dilution control system,analyze structure of pulp distributor,dilution module and intelligent actuator,discusses the design principle and points.Through the analysis of the traditional design principle of the pulp distributor,point out the problems in the design,and put forward the new design method with segmented Baines equation in wide high-speed headbox.For the response speed,control accuracy and stability of intelligent actuator,developed technology of the closed-loop feedback control of digital position,the automatic gap compensation,automatic valve correction and position power-off memory.By analyzing the nonlinear relationship between the position and flow of the dilution valve,put forward the linear flow compensation method.According to the message characteristics of intelligent CD control,the CAN bus communication architecture of the intelligent actuator was developed and the extended frame data structure of the CAN communication message was customized to improve the reliability of the control system.Fourthly,the dilution response model and step response method were studied.According to the problems in the traditional step identification method,an improved IRLM algorithm was presented by modifying the target error function and the matrix inversion,so as to identify the steady state response model and dynamic response model in real time.The model identification of the IRLM algorithm was carried out chaos time-series prediction experiment and performed on the paper machine.The results showed that the convergence speed of the residuals was faster than the traditional identification method.To solve the problems of the large-scale,strong coupling and large time-lags properties of the CD control processes,the controllability of the CD control system was analyzed.The spatial frequency decomposition technology was introduced to analyze the cyclic symmetry structure of steady state model.The two-dimensional internal model controller based on spatial frequency decomposition technology was designed.The large-scale CD controller was decomposed to a series of single-variable controller with spatial frequency index,which gave them a deeply analysis to comprehend robust stability,steady state and dynamic performance of the internal model controller.Finally,an intelligent CD control system based on CAN bus and OPC technology was designed to deal with the distributed and coordinated characteristics of CD control.The two-layer control network of Ethernet and CAN bus was improved the real-time control and system scalability.The model identification and CD algorithm were closed-loop controlled by the main control station through the measured data,and the measured data and monitoring data were synchronized and shared by OPC technology.The intelligent actuator,model identification and CD algorithm were applied to the domestic high-speed paper machine,and the feasibility and validity of the system were verified by practical applications.