Looper System Research Articles

Reinforcement-Learning-Based Composite Optimal Control for Looper Hydraulic Servo Systems in Hot Strip Rolling

The control scheme of the looper angle plays an essential role in hot rolling, which is directly related to the tension maintenance of the strip. The conventional scheme uses a proportion–integration–differentiation (PID) controller to control the servo valve to drive the hydraulic actuator. For different steel types and production temperature changes, the PID control mainly relies on empirical parameter adjustment, which may bring inaccuracy or inefficiency. The objective of this article is to propose a reinforcement-learning-based looper hydraulic servo optimization control scheme to automatically tune the control gain to optimum. First, the modeling error caused by variable parameters and the influence of external disturbance are considered, and the corresponding control model of the looper system is given. Subsequently, a feedforward controller with a radial basis neural-network-based disturbance observer is used to deal with modeling errors and disturbances. A feedback controller with off-policy reinforcement learning is applied in the meantime. The proposed control scheme can realize uniformly ultimately bounded of the system with Lyapunov theory. Simulation results verify the effectiveness of the proposed method.

루퍼시스템 응답의 자동진단기술

This paper proposes an algorithm to automatically diagnose the looper angular response characteristics of a looper system installed in multi-stand type rolling mills in real time. The looper angular response pattern is clearly distinguished three operating areas such as the front part, the controlled part, and the back part. There are two key techniques that compose diagnosis algorithm. First, physical indicators including information on the physical state for each part were designed. Second, the performance indexes, which means the current state of each part numerically, were suggested in the form of a judgment formula using physical indicators. According to the simulation results, the proposed diagnosis algorithm computed each performance index for given the looper angle response data and gave information on the presence or absence of abnormality and the abnormal part of the looper angle response.

Correlation analysis between looper system and strip width narrowing in hot strip rolling

Correlation analysis between looper system and strip width narrowing in hot strip rolling

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.

Parametric Robust Control of the Multivariable 2 × 2 Looper System in Steel Hot Rolling: A Comparison between Multivariable QFT and H∞

Two robust mutlivariable controllers, H∞ and a decentralized quantitative feedback theory (QFT), are designed in the frequency domain for the 2 × 2 looper system in a steel hot rolling mill to keep stability in the presence of parametric uncertainties. The H∞ controller is designed by using the mixed sensitivity approach, while the multivariable decentralized QFT is designed by the extension of the sequential loop closing method presented elsewhere. Stability robustness conditions are verified in the frequency domain, while simulations in time domain are carried out to evaluate the controllers and compare their performance along with that of proportional + integral (PI) and single input single output (SISO) QFT controllers designed earlier. The QFT controller shows the best balance among the performance indicators analyzed here; however, at the expenses of using higher power in one of the control inputs.

Dynamic matrix predictive control for a hydraulic looper system in hot strip mills

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 work describes a dynamic matrix predictive control (DMC) strategy that realizes the optimal control of a hydraulic looper multivariable system. Simulation experiments for a traditional controller and the proposed DMC controller were conducted using MATLAB/Simulink software. The simulation results show that both controllers acquire good control effects with model matching. However, when the model is mismatched, the traditional controller produces an overshoot of 32.4% and a rising time of up to 2120.2 ms, which is unacceptable in a hydraulic looper system. The DMC controller restricts the overshoot to less than 0.08%, and the rising time is less than 48.6 ms in all cases.

Multivariable Decoupling Control of Hydraulic Looper System Based on ADAMS-MATLAB Co-simulation

Multivariable Decoupling Control of Hydraulic Looper System Based on ADAMS-MATLAB Co-simulation

Guaranteed cost sliding mode control for discrete-time looper systems in hot strip finishing mills

A guaranteed cost sliding mode control (SMC) algorithm is investigated to further improve the control accuracy of looper-tension systems in hot strip finishing mills. First, a global sliding mode surface function is designed by linear matrix inequalities and guaranteed cost technique, which can force the system states into switching region initially, and can guarantee the system robustness with a good performance during the whole control process. Then, a novel reaching law is designed, which can satisfy the sliding mode reaching conditions. Simulation results demonstrate that the proposed control scheme has good stability and robustness comparing with traditional SMC. The designed controller can regulate the strip tension and looper angle to ensure better performance, which is very suitable for complex looper systems.

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.

Improved Relative-transformation Principal Component Analysis Based on Mahalanobis Distance and Its Application for Fault Detection

Principal component analysis (PCA) has been widely used in process industries, which could maintain the maximum fault detection rate. Although many issues have been addressed in PCA, some essential problems remain unresolved. This study improves PCA for fault detection performance in the following ways. Firstly, a relative transformation scheme based on Mahalanobis distance (MD) is introduced to eliminate the effect of dimension of data instead of dimensionless standardization, and improve the accuracy and real-time performance of fault detection. The theoretical derivation proves that relative transformation based on MD can directly eliminate the effect of dimension and give reasonable explanation of PCA in the relative space, the analysis and simulation results show its superiority and effectiveness. Secondly, an improved squared prediction error (SPE) statistic is given to improve the fault detection performance of standardized PCA, which can make the standardized PCA-based fault detection method more suitable for the actual industrial process. Finally, two improved methods are combined to detect the fault more effectively. The proposed methods are applied to detect single fault and multi-fault of looper system in hot continuous rolling process, simulation results demonstrate the effectiveness of these improvements for fault detection performance in terms of sensitiveness, accuracy and real-time performance of fault detection.

Decoupling Control Research of the Strip-Cast Looper Height and Tension QDRNN Network

Based on the classical cast theory and modern hot continuous rolling theory, in order to improve further the thickness precision of casting and control quality, so the dynamic mathematical model of strip-cast Looper system was established, which is nonlinear, strong coupling and uncertainty. According to the actual data, the comparative complete transfer function of Looper system is calculated. And the QDRNN-PID control strategy is put forward to subtract the coupling effect of Looper system. The simulation results prove that this control strategy can obtain a better control effect of Looper system after decoupling.

Approximate Dynamic Programming-Based Approaches for Data-Driven Control of Hydraulic Looper System

Approximate Dynamic Programming-Based Approaches for Data-Driven Control of Hydraulic Looper System

Adaptive Learning and Control for MIMO System Based on Adaptive Dynamic Programming

Adaptive dynamic programming (ADP) is a promising research field for design of intelligent controllers, which can both learn on-the-fly and exhibit optimal behavior. Over the past decades, several generations of ADP design have been proposed in the literature, which have demonstrated many successful applications in various benchmarks and industrial applications. While many of the existing researches focus on multiple-inputs-single-output system with steepest descent search, in this paper we investigate a generalized multiple-input-multiple-output (GMIMO) ADP design for online learning and control, which is more applicable to a wide range of practical real-world applications. Furthermore, an improved weight-updating algorithm based on recursive Levenberg-Marquardt methods is presented and embodied in the GMIMO approach to improve its performance. Finally, we test the performance of this approach based on a practical complex system, namely, the learning and control of the tension and height of the looper system in a hot strip mill. Experimental results demonstrate that the proposed approach can achieve effective and robust performance.

Linear multivariable dynamic model of a hot strip finishing mill

A steel hot strip finishing mill presents significant interactions between variables that considerably reduce performance. Traditionally, the control techniques implemented are based on classical approaches assuming an ideal model. Modelling interactions would allow the opportunity to suppress them by the application of modern multivariable control techniques. In this paper the derivation of a linearized multivariable model of a real-life hot strip mill based on previous schemes is presented as a case study. Linearization of the non-linear static relations around an operating point is performed. The operating conditions are the mill set-up calculations obtained from rolling schedules and non-linear relations used in the plant. Some useful details for practitioners are given. Simulations and experimental model validation are also presented. Since the mill in the real hot rolling line is in closed loop, it is not possible to carry out an experimental validation of the plant itself (i.e. in open loop); therefore, the model was experimentally validated in closed loop. As an example of the use of the multivariable model an H∞ multivariable optimal controller to attain nominal performance is designed for the looper system and results are presented.

열연 루퍼시스템의 퍼지 장력제어

The hot rolling process ranks the highest position for production in steel making process. The hot strip manufacturing processes consist of the reheating furnace, roughing and finishing mill and coiler. The reheating furnace heats the slab. The roughing and finishing mill produce the hot strip from slab. The hot strip quality mainly depends on finishing mill, which consists of 4-high 7 stands. The looper is installed between stands and is used for controlling the strip tension by the looper angle for better material flow. It is difficult to control the strip tension with the coupled looper system from interaction between the looper angle and strip tension. Too much deviation of strip tension severely affects the poor width quality of the hot strip. It is important to control simultaneously both the looper angle and strip tension with each of their target values. This paper proposes the fuzzy tension control, which is developed to minimize the width deviation of the hot strip by maintaining the proper strip tension between stands and to achieve the stable operation of the coupled looper system. The fuzzy tension control performance is compared with the conventional PID control by experimental results.

Based on Nonlinear Disturbance Observer Approach Non-interactive Control for Hot Rolling Mill: Experimental Validation

This paper proposes an advanced method to reduce fluctuations of strip tension and looper position in a steel rolling mill. We design a non-interactive controller to decouple the looper system into two subsystems. We consider uncertainties, disturbances and interactions as each nominal subsystem's disturbance. To reduce these disturbances, we use a nonlinear disturbance observer. We prove that the proposed method can reduces response time and fluctuations in strip tension in comparison with other methods. Simulation results and hardware experiment results are included.

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

Dynamic Simulation of AGC/LPC Synthetical System for Hot Strip Finishing Mill

A simulation of hot strip finishing mill automatic gauge control (AGC) system is built, which is divided into four modules such as rolling mill system, AGC module, looper system and strip model. The rolling mill system is built by mechanism modeling, the looper system and strip model are built by function modeling, and the AGC model is tried to use intelligent control of a multi-function AGC system. The target is attempted to use this simulation object to minimize finisher exit strip thickness deviation resulting from strip entry thickness disturbance and rolling force deviation. Simulation results show that the result of this AGC/LPC synthetical system module simulation is quite close to the actual result. The simulation system can also analyze most kinds of disturbance which affect the rolling process. It is proved that the system can represent practical situation of hot strip finishing mill process control, and be used as a basic platform of research and development for researcher and engineer.

RHC를 기반으로 하는 열간압연 루퍼 제어

In this paper, a new looper controller is proposed to minimize the tension variation of a strip in the hot strip finishing mill. The proposed control technology is based on a receding horizon control (RHC) to satisfy the constraints on the control input/state variables. The finite terminal weighting matrix is used instead of the terminal equality constraint. The closed loop stability of the RHC for the looper system is analyzed to guarantee the monotonicity of the optimal cost. Furthermore, the RHC is combined with a 4SID(Subspace-based State Space System Identification) model identifier to improve the robustness for the parameter variation and the disturbance of an actuator. As a result, it is shown through a computer simulation that the proposed control scheme satisfies the given constraints on the control inputs and states: roll speed, looper current, unit tension, and looper angle. The control scheme also diminishes the tension variation for the parameter variation and the disturbance as well.

Tension control in hot strip process using adaptive receding horizon control

This paper presents a new looper–tension control scheme to minimize the tension variation between two stands in the hot strip finishing mill. The proposed control scheme is designed on the basis of a 5th order state space model for a looper system and composed of two main parts. First, a receding horizon control (RHC) feedback controller with a minimal-order disturbance observer (DOB) is employed to satisfy the constraints on the control input/state and guarantee the stability. The observer is also designed for attenuating the speed disturbances of the main motor. Second, a subspace-based state space system identification (4SID) model identifier is introduced to adopt the variation of system parameters. It is shown through simulation that the proposed control scheme satisfies the constraints on the control input/state, diminishes the tension variation for the parameter variation and the speed disturbances, and reduces the computational burden for the model adaptation as well.