Looper Control System Research Articles

Dynamic modelling and linear quadratic sliding mode control of a multivariable looper system in hot strip mills

This paper introduces a linear quadratic sliding mode control (LQ-SMC) scheme into a looper control system. First, according to a 1700 mm tandem hot mill, the state-space dynamic model of the looper system was established, and then, the optimal control law of the looper system was obtained based on the established model. Finally, the optimal sliding mode and optimal sliding mode control law of the LQ-SMC scheme were designed such that the sliding motion could satisfy the optimal value of the quadratic performance index. Simulation results show that the proposed control scheme has complete robustness to external disturbances that satisfies certain conditions, and the coupling between the looper angle dynamic and strip tension dynamic is also minimized.

Consensus Control for Looper Tension Control System Using Subspace Identification Method

The looper tension control system of hot strip mills is a typical multi-agent system, and the coupling effects among the agents are strong. However,it is difficult for us to establish the accurate coupling model for the looper tension control system. In this study, a distributed control strategy is proposed for the looper tension control system. With the subspace identification method, the local measurement of the looper control system and the information of its neighbors are used directly to develop the consensus control protocol without any knowledge of the looper tension system dynamics. The sufficient conditions for the consensus of multi-agent system with the proposed control protocol are proposed. In addition, a consensus control protocol with communication time delay is presented. Finally simulations are performed to verify the effectiveness of the control strategy.

An Output Probabilistic Constrained Optimal Control Algorithm Based on Multivariable MAC and its Application in Looper Control System

Most actual industrial processes are multivariable and constrained complex systems. The state and output of the system also have uncertainty due to the existence of random disturbances. The output of the system is easier to be measured than the state and can more intuitively reflect the running state of the system. Considering the limitations of industrial equipment and the benefits of production, it is generally allowed to have a small portion of the output that can exceed the constraints. As a result, the outputs can be represented as corresponding single probabilistic constraints. In this paper, therefore, an output probabilistic constrained optimal control algorithm based on multivariable model algorithm control (MMAC) is proposed. First, the feedback correction link of the MMAC algorithm is improved, and the predicted outputs are corrected by taking the weighted average of the errors. Then, assuming that the disturbances obey Gaussian distribution, the output probabilistic constraints are transformed into deterministic ones. Next, the optimal control problem is solved as a quadratic programming (QP) problem after combining them with the performance index function of the MMAC. Finally, the proposed algorithm is applied to the looper control system in hot strip rolling process and compared with the single MMAC algorithm to verify its effectiveness.

Robust decoupling mixed sensitivity controller design of looper control system for hot strip mill process

This article considers a robust decoupling controller design for a multivariate control system with parameter uncertainties for the hot rolling mill process. The left and right coprime factorization theory is used to properly select the free and weighting matrices. The necessary and sufficient conditions for robust decoupling controller are also proposed. Then, by analyzing the changes in the dynamic response resulting from perturbations in the tension and angle system parameters in the hot strip rolling process, a modified multivariate model is developed. Furthermore, the selection method for a practical weighting function is studied, so that the robust and decoupling performance can be simultaneously realized for the controller implementation. Finally, the effectiveness of the proposed control approach is demonstrated using a case study from an industrial hot rolling mill.

Modeling and multivariable active disturbance rejection control of hydraulic looper multivariable system

Controlling the looper height and strip tension is important in hot strip mills, because these variables affect both the strip quality and strip threading. Many researchers have proposed and applied a variety of control schemes for this problem, but the increasingly strict market demand for strip quality requires further improvements. This paper describes a multivariable active disturbance rejection control (MADRC) strategy that realizes the decoupling control of a hydraulic looper multivariable system. Simulation experiments for a traditional proportion- integration (PI) controller and the proposed MADRC controller were conducted using MATLAB/Simulink software. The simulation results show that the proposed MADRC ensures good robustness and adaptability under modeling uncertainty and external disturbance .It is concluded that the designed MADRC controller produces better dynamic performance than the traditional PI controller, and the proposed looper control system is effective and practical.

Decoupling Control and Simulation of Looper MIMO System for Hot Strip Rolling Mill

An optimal multivatiable looper control system based on decoupling strategy has been developed for hot strip finishing mills. Based on the dynamic configuration of the coupling system, we can get the status space expression of the coupling loopers system. Through the tools of Matlab we make out of the transfer function of looper system. Based on Decouping-Inbariable character theory and the transfer function of looper system we gain the transfer function of the decoupling net. By using the Simulink toolbox of the Matlab language, the simulation results have shown that, after decoupled, the loopers control system performance gets much better.

Design and Application of a Class of Multiplexed Receding Horizon Controllers for Looper Control System

摘要: 针对热连轧活套高度和张力的双输入双输出强耦合系统, 文中提出一类基于滚动时域优化原理的多路控制策略. 基于滚动优化原理, 在每一个周期内, 顺序求解子系统的控制律后及时更新系统. 从H∞观点出发, 将解耦问题转化为干扰抑制和多目标优化问题, 能够减轻计算机的负担, 提高控制系统的性能. 仿真结果证实了该方法具有良好的解耦效果和控制性能. 关键词: H∞控制 / 预测控制 / 活套控制 / 解耦控制

Modeling and Integral Variable Structure Control of Hydraulic Looper Multivariable System

摘要: 为了实现热连轧中活套高度与张力系统的解耦控制, 需对具有非线性、强耦合、不确定、多约束特性的活套系统建立工程上适用的数学模型. 通过对活套系统动态耦合过程的分析, 在工作点附件, 结合伺服阀和液压缸的模型, 建立起液压活套系统的动态数学模型. 采用积分滑模变结构多变量解耦控制策略以减弱系统的耦合影响, 提高控制效果. 仿真结果验证了本算法的有效性, 表明解耦后的活套控制系统可获得更好的控制效果. 关键词: 活套系统 / 解耦 / 建模 / 数学模型 / 滑模变结构控制

Adaptive and Robust Control Method with Estimation of Rolling Characteristics for Looper Angle Control at Hot Strip Mill.

In this paper, an adaptive robust control method for looper height control of hot strip finishing mill is proposed. The change in strip tension, which exerts an influence on the width and thickness of the products, is induced by the looper height variation. Accordingly, it is important to control the looper height precisely. The looper control system may suddenly become unstable due to a change in the characteristics of rolled material and an occurrence of the slip between roll and strip while rolling. In order to maintain the control system stable even under these changes, the robust control system has been developed. However, there remained problems of slow response of the robust controller. The reason is that the control gain is set at a low value to assure the stability for the various kinds of disturbances. To solve the problem, it is necessary to set at the appropriate control gain. In this paper, the estimation of a damping coefficient of the looper height control system is carried out to adapt the control gain according to the damping coefficient. The proposed adaptive controller assures both the robustness and a high control performance regardless of the change in rolling conditions and disturbances. Using this method, the looper height control can guarantee both the stability of the looper height control and the high degree of accuracy in control.

Fuzzy algorithm for calculating roll speed variation based on roll separating force in hot rolling

Thickness control of hot-rolled strips has become an important issue in recent years because of the need for improving the quality of the hot-rolled strip. For this purpose, various thickness control systems such as finishing mill set-up (FSU), automatic gauge control (AGC), and looper control system, have been developed at steel works. Although these systems have greatly improved the quality of the strip thickness, there still exists a small amount of thickness deviation. It is difficult to adequately control by applying conventional thickness control techniques since hot rolling process is a highly nonlinear system in which many process parameters are coupled. In this study, a fuzzy algorithm to calculate the roll speed variations was developed in order to improve the thickness uniformity of hot-rolled strips. Since the strip thickness is mostly affected by the magnitude of roll separating force depending on the roll speed, the strip thickness deviation between the desired and actual thicknesses can be reduced by controlling roll speed. In order to carry out this investigation, slab analysis was carried out to determine the relation between roll separating force and roll speed for various process parameters such as roll speed, reduction ratio, strip entry thickness, and front and back tensions. From the production data, the effective stress-strain rate relations of the materials used in slab analyses were acquired. Based on the analytical results, the relation between roll separating force and roll speed was approximated by a log function. A fuzzy algorithm was developed to determine variations in roll speed according to variations of roll separating force, depending on various ranges of rolling temperature, reduction ratio, front and back tensions, and strip thickness. In addition, simulations to predict roll speed variations for a small amount of thickness deviation were carried out at continuous finishing mills consisting of seven stands and the calculated roll speed variations were found to be reasonable. Thus, the developed fuzzy algorithm might be useful in reducing the thickness deviation in the actual hot rolling mills.

Optimal multivariable looper control for hot strip finishing mill

An optimal multivariable looper control system based on optimal-regulator theory was developed for hot strip finishing mills. Loopers of a hot strip finishing mill are installed between stands and are, in many cases, driven by motors. The goal of looper control is to maintain product quality at a high level by stabilizing the rolling operation. Stability is achieved by keeping the looper angle and tension applied to the strip at given reference values. The most difficult problem is mutual interaction in the simultaneous control of looper angle and strip tension. In particular, increasing use of low-temperature heating of slabs, high-carbon steels, and high-speed rolling places additional demands on the looper control system. Moreover, high quality of thickness, width, and crown are strongly requested. Controlling the rotational speed of the looper motor in addition to the existing looper motor current control has allowed a robust looper control system that can cope with changes in rolling conditions. Based on the current rolling conditions, the system selects the control gain calculated from different weight matrices for the linear quadratic criterion. The developed control system can maintain relatively constant strip tension without operator intervention in the presence of rapid changes of hydraulic screwdown, such as automatic gage control (AGC) operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hot Strip Mill Looper Direct Digital Control System

A high level of accuracy and quick response are required in the looper control to keep up with the changes in the operational conditions in modern hot strip mills, such as operation at higher speed and rapid acceleration on the finishing mill and bigger skid marks, and to achieve improvements in the dimensional accuracy of the products (thickness (gauge) and width) and in the yield rate.The old looper control system at the hot strip mill in Kakogawa Works has consisted of analog circuits until now. Despite their constant height and tension-control capabilities, there were some instances where they failed to cope with such changes in the operational conditions as mentioned above owing to their rather unreliable control performance.Recently, since the looper analog control system has been replaced with a DDC (direct digital control) system which consists of μ-computer, a high level of accuracy control has been achieved through the precise calculations of the control parameters, which are based on the data on rolling conditions such as the rolling mills, the screwdowns and the looper drives, and on the information obtained from the main process computer.Appreciable improvements in both the quality of products and the yield rate have been accomplished through the use of this new system and the details of the control performance are discussed.