Multivariable Decoupling And Time-Delay Control Strategies For Cross-Directional Basis Weight Of Papermaking Process

Basis weight is the quality of paper per unit area and it is one of the most important indicators for evaluating paper quality.With the improving requirements of consumers to the quality of paper products and the introduction of the high speed printers,more rigorous performances to the fiber uniform distribution of paper sheet are suggested.Only the machine directional(paper machine running direction)control can not guarantee the paper quality.Cross directional(CD)control plays a more important role in uniform distribution.The uniformity of cross directional basis weight distribution is not only related to the quality of the paper itself,but also greatly affects the production efficiency and raw materials consumption.In order to explore the effective ways to solving the difficulties of high-dimensional large system,coupling and time delay and space-time dislocation in cross directional process.A research on the paper cross directional basis weight on-line intelligent control strategy based on dilution water headbox is carrying out in this paper.This work is partially supported by the science and technology co-ordination project of Shaanxi Province and the key scientific research and innovation team project of Shaanxi Province.The contributions of the study were shown as follows.?.Research on the pulp consistency regulation model and the slurry flow pattern in dilution water headbox.Cross-directional basis weight of paper based on hydraulic headbox is adjusted by the opening of dilution water valve.In order to achieve uniform concentration distribution of paper sheet,a research on the effect of dilution water added to the mainstream on concentration and flow was studied by experimental set-up and mathematical modeling in this paper.Firstly,based on the numerical simulation results,a scale model of headbox was derived to predict the water content distribution and pulp consistency distribution.Results show that these models could accurately predict the experimental flow characteristics of a pulp suspension with dilution water added.Secondly,based on the concentration dilution mathematical model of hydraulic headbox,comparing the regulation of the slice lip actuator with dilution water valve,the principle of reverse response is analyzed.Though parameters improvement of pulp consistency model,the reverse response on both sides could be well eliminated or balanced when the dilution water was adopted to CD profile control system.It ensures that the influence range of a single dilution water valve was controllable,which improves the adjustment accuracy of cross-directional profile control and thus improves the paper quality.?.Research on the multivariable dimension-reduction and interpolate decoupling strategy for CD basis weight of papermaking process.In view of the characteristics of strong multivariable coupling in a CD basis weight control system,a multivariable block-decoupling control strategy and a real-time decomposition algorithm are proposed in this paper.Based on a model of the CD basis weight profile,a system non-square interaction matrix with high dimensionality was analyzed by experimental studies and numerical computation.Along the diagonal of the interaction matrix,the matrix block method was adopted to reduce the system dimensions and convert it into a square system.The multivariable control system with high dimensionality is divided into several subsystems.According to the structure of each subsystem,a new constraint on the control variables was introduced to satisfy the triangular decomposition of the subsystem.Based on the multi-actuator parallel control strategy,the correlation between the subsystems was eliminated,and a high-dimensional non-square system was transformed into a square coupling system.For the high-dimensional Toeplitz symmetric systems with small-scale coupling characteristics,an interpolation algorithm is proposed.Then a symmetric Toeplitz decoupling matrix was obtained.Comparing with the conventional diagonal decoupling,the number of new decoupling branches is reduced from 2408 to 186,which greatly reduces the number of decoupled network branches and realizes fast decoupling of multivariable systems.By designing the diagonalized controller for the decoupled new system,a decoupled cross directional control system for corrugated paper with a basis weight of 130g/m2 was completed,ald the real-time performance of the technique was demonstrated by results from an implementation on an actual project of a paper mill.?.Study on the control strategy for the large scale single loop with the time-delay.Due to fluctuations in the speed of the paper machine,the control unit of CD basis weight exhibits time uncertainty characteristics.Therefore,for the time-delay control strategy of CD basis weight process,not only the validity,convergence and stability of the algorithm should be considered,but also the robustness and real-time of the algorithm.In this paper,the controller of the Smith control structure is designed for a single-loop group system,which consist of 64 similar time-delay models.Based on the H? control theory,the expression of the parameter tuning of the main controller of the Smith predictor is obtained by minimizing the sensitivity function.This ensures that the closed-loop system has sufficient robust stability and good control performance.As the control effect of the H? controller decreases with the increase of delay,a two-degree-of-freedom Smith predictor based on fractional order PID controller is proposed in this paper.It has the capability to control the set value track and load disturbance independently.Fractional order PID controller with strong anti-interference and robustness is served for load disturbance.Simulation results show that the two-degree-of-freedom Smith predictor can effectively restrain the influence of the delay time on the stability of the system,and improves the robustness effectively when the model mismatched.?.Research on the CD basis weight data reconstruction of compressed sensing method and space-time alignment method of actuator.The scanning sensor measures the amount of paper in the cross direction of the paper.As the paper moves vertically,the scanning sensor can only measure the "Z" shape area on the paper.When the scanning frequency is not at least twice the maximum frequency of the paper variation,it becomes difficult to estimate the sheet profile.To overcome this limitation,a data reconstruction method based on compressed sensing is proposed.The CD fluctuation model is identified by the reconstructed data and the original data respectively,then the data reconstruction effect of the compressed sensing method was verified.Based on the reconstructed data,the CD and MD basis weight data are separated by the predictive separation algorithm.It ensures the basis for CD control.Exact mapping between actuator and scanner databox of the sheet profile is an essential precondition for CD control.Special weight is given to how identify the alignment from input-output process data.In this article,a technique for CD alignment identification is proposed.Based on the process data obtained by bump test,The CD process is modeled and identified by fitting a non-linear parametric model to the bump test data.The corresponding mapping relationship is developed by determining the profile response centre,calculating the response width and analyzing the relative response amplitude.Due to the sheet shrinkage and web drift in the cross direction,it is not known which actuator is working in the profile.A method that identifies this relationship by means of clustering analysis and statistical analysis for physical mapping data is proposed in this paper.Misalignment compensation measure are activated to self-tuning the alignment,and adjust mapping parameters in real time to adapts cross-direction control,which improves the adjustment accuracy of CD profile control and thus improves the paper quality.V.Design and implementation of the CD control system.On the basis of aboard advanced CD control system,an specific implementation scheme of CD profile control system is designed.With Siemens S7-300 controller as the main hardware,Step7 and WinCC as the software development platform,as well as the help of OPC protocol and Industrial Ethernet communication.The scheme combines existing QCS system of the pilot papermaking enterprises,and the implementations of algorithms are based on Matlab.The engineering application results show that the scheme to be effective,the CD basis weight distribution is improved.To sum up,the technical problems of multivariable decouping and large scale time delay control for the paper basis weight control has been solved.A general method for transforming high-dimensional multivariable control problems into single-loop group control problems.Based on the fast decoupling strategy of the nonlinear high-dimensional sparse correlation matrix with small range coupling characteristics and the online real-time robust control algorithm for large-scale time-delay loops,the CD basis weight control based on hydraulic headbox with dilution water are solved.The basis weight indicators could be controlled within the range of 2%,which could meet the precision requirement of basis weight control in production,even could be suitable for to replace import products.It provides theoretical reference for the localization of paper basis weight control system.