Automatic Gauge Control Research Articles

Absolute Stability Condition Derivation for Position Closed-Loop System in Hydraulic Automatic Gauge Control

In the metallurgical industry, hydraulic automatic gauge control (HAGC) is a core mechanism for thickness control of plates used in the rolling process. The stability of the HAGC system’s kernel position closed-loop is key to ensuring a process with high precision, speed and reliability. However, the closed-loop position control system is typically nonlinear, and its stability is affected by several factors, making it difficult to analyze instability in the system. This paper describes in detail the functioning of the position closed-loop system. A mathematical model of each component was established using theoretical analysis. An incremental transfer model of the position closed-loop system was also derived by studying the connections between each component. In addition, based on the derived information transfer relationship, a transfer block diagram of disturbance quantity of the system was established. Furthermore, the Popov frequency criterion method was introduced to ascertain its absolute stability. The results indicate that the absolute stability conditions of the position closed-loop system are derived in two situations: when spool displacement is positive or negative. This study lays a theoretical foundation for research on the instability mechanism of an HAGC system.

Bifurcation Characteristic Research on the Load Vertical Vibration of a Hydraulic Automatic Gauge Control System

As the core control system of a rolling mill, the hydraulic automatic gauge control (HAGC) system is key to ensuring a rolling process with high speed, high precision and high reliability. However, a HAGC system is typically a mechanical-electric-hydraulic coupling system with nonlinear characteristics. The vertical vibration of the load easily occurs during the working process, which seriously affects the stability of the system and the causes are difficult to determine. In this work, the theory and method of nonlinear dynamics were employed. The load vertical vibration model of the HAGC system was established. Then, the multi-scale method was utilized to solve the obtained model, and the singularity theory was further applied to derive the transition set. Moreover, the research object of this article focused on some nonlinear factors such as excitation force, elastic force and damping force. The effects of the above feature parameters on bifurcation behavior were emphatically explored. The bifurcation characteristic of the load vertical vibration of the HAGC system was revealed. The research results indicate that the bifurcation curves in each sub-region, divided by the transition set, possess their own topological structure. The changes of the feature parameters, such as the nonlinear stiffness coefficient, liquid column height, nonlinear damping coefficient, and external excitation have an influence on the vibration amplitude of the HAGC system. By reasonably adjusting the nonlinear stiffness coefficient to effectively avoid the resonance region, the stability of the system will be facilitated. Furthermore, this is conducive to the system’s stability as it properly controls the size of the liquid column height of the hydraulic cylinder. The appropriate nonlinear damping coefficient can decrease the unstable area, which is beneficial to the stability of the system. However, large external excitation is not conducive to the stability of the system.

Improving the mechatronic system for automatic control of the reversing stands of mill 5000

It is noted that when extending the range of products made by plate rolling mills, it becomes relevant to improve the algorithms of the automatic parameters control systems. We hereby present a structure that explains the SMS Demag AG concept of automatic control over stand roll gauge and gaps. This concept is implemented in the automatic gauge control system (AGCS) of Mill 5000, Magnitogorsk Iron and Steel Works. We describe the drawbacks of the AGCS that manifest when rolling <10 mm plates. The most serious drawback is the tear of metal pieces from the trailing edge, which is caused by the inappropriate functioning of the gauge assignment and adjustment system. We present the structural diagram of the gauge calculation system. We also describe the functions of a system for dynamic compensation of disturbances. We provide rationale for excluding the roll counter-bending and deformation correction signals. The paper proposes a method to control hydraulic screwdowns, which is essentially about a quick increase in the inter-roll gap at the workpiece “trailing edge” during the last pass, which must be done when rolling thin plates. We analyze the oscillograms of signals describing the gauge interference when the proposed changes are implemented. We prove the technological efficiency of using the proposed control method on Mill 5000.

Nonlinear Backstepping Control Design using a High Gain Observer for Automatic Gauge Control

The accuracy and quality of the steel strip exit thickness depends on the structure of the automatic gauge control system (HAGCS) of reversible cold rolling mill. This structure is based on the position control of the work rolls. The design and implementation of a new HAGCS by the backstepping approach with high gain observer are discussed in this paper. Backstepping controller of HAGCS and high gain observer (HGO) has been implemented using MATLAB/SIMULINK software. The simulation results show the effectiveness of the proposed control for improving the quality of the output strip.

Amplitude-frequency characteristics analysis for vertical vibration of hydraulic AGC system under nonlinear action

Hydraulic automatic gauge control (AGC) system is the core control system to ensure the thickness accuracy of cold-rolled plate, and the reliability of its load roll system is the key to guarantee the rolling process with high precision, high speed, continuity and stability. However, the working mechanism of hydraulic AGC system is complex. And it possesses some features such as high nonlinearity, time variability and strong coupling. The vertical vibration easily happens in its working process. Moreover, the stability of system is seriously affected. Nevertheless, the incentive is difficult to determine. In this paper, the theory and method of nonlinear dynamics were introduced to establish the load vertical vibration (LVV) model of HAGC system under nonlinear action. The model was solved with multi-scale method, and the amplitude-frequency characteristic equation of system was obtained. Moreover, the research object of this article also focused on the nonlinear elastic force, nonlinear damping force and nonlinear excitation force, and deeply explored the effect of nonlinear parameters change on the amplitude-frequency characteristics of LVV system. The mechanism and incentive for LVV of hydraulic AGC system were further revealed. The research results lay a theoretical foundation for the vibration inducement and suppression of hydraulic AGC system.

Characteristic analysis and optimal control of the thickness and tension system on tandem cold rolling

The tandem cold-rolling process is a multivariable, nonlinear, and strongly coupled complex control procedure, in which the key technologies of automatic gauge control (AGC) and automatic tension control (ATC) are extremely comprehensive, and high precision is required. This paper analyzes the rolling characteristics of tandem cold-rolling process and proposes an innovative multivariable optimization strategy based on inverse linear quadratic (ILQ) optimal control theory for thickness and tension control. First, a new state space model of the tandem cold-rolling process was introduced and verified based on the basic equations of rolling technology and field data. Then, meaningful influence rules on the complex rolling process were obtained by analyzing rolling characteristics. For the complex rolling process, a novel ILQ control strategy was introduced into the thickness and tension control system. As a result, by a series of experiments, the effect of disturbance on the thickness and tension was attenuated to an arbitrary degree of accuracy through the proposed control strategy. Simulation results showed the excellent control performance of the proposed ILQ control strategy compared with the conventional proportion and integration (PI) control strategy.

Mathematical Modeling of Mechatronics System "Hydraulic Screwdown Mechanism - Electric Drive of Rolling Mill Stand"

The article provides a rationale for the mathematical model of a mechatronics system "hydraulic screwdown mechanism - electric drive of a rolling mill stand". The authors emphasized the relevance of the research of the developed method to limit dynamic loads imposed on electromechanical system rolls in compliance with which a roll gap is increased before metal bite and roll movement to a set position during rolling. The paper presents a block diagram for a complex mathematical model including local models of a hydraulic screwdown mechanism in the automatic gage control system (AGCS) and a rolling mill stand structure interconnected by metal. Further, the setup of a system for the adjustment of the screwdown mechanism position is considered. The authors provide analytical dependences to calculate the specific roll force and mill torque. The developed method was modeled, and it was proved that its implementation results in the decrease of the dynamic torque at metal bite. The article is concluded with the recommendations on the developed model use.

Optimization-based feedforward control of the strip thickness profile in hot strip rolling

A new feedforward control approach for the thickness profile of the strip in a tandem hot rolling mill is developed. In industry, the automatic gauge control (AGC) concept is widely used for thickness control. The AGC has the disadvantage that it does not consider known disturbances from upstream entities. This is why a number of disturbance feedforward control concepts have been proposed in the literature. These feedforward control strategies typically rely on linearized models and only provide symmetric control inputs for the mean thickness to the hydraulic adjustment system. In this work, an optimization-based feedforward controller for the lateral thickness profile is proposed that fully exploits all degrees of freedom available, i.e., the hydraulic cylinder positions and the bending forces at the drive side and at the operator side of the mill stand. Moreover, it is shown that by linearizing the mill stand model while keeping the nonlinearities from the roll gap model leads to a numerically efficient optimization problem, which is a good compromise between accuracy and computational efficiency. The feedforward controllers are further combined with the AGC in the feedback path in a two-degree-of-freedom controller structure to account for model-plant mismatch. Simulation results for a validated mathematical model and first experimental results from an industrial pilot installation show a significant benefit compared to the existing AGC without feedforward control.

Automatic Gauge Control under Laterally Asymmetric Rolling Conditions Combined with Feedforward

The most common and well proven control strategy for thickness control in industrial rolling mills is the automatic gauge controller (AGC). However, it is still unclear how to use AGC for the control of asymmetries in lateral direction. How should the controller react to different thickness estimations at both sides of the mill? Such laterally asymmetric rolling conditions may originate from strip track-off, asymmetric friction in the mill stand, or a wedge-shaped entry profile of the strip thickness. In this paper, three control approaches are discussed. Two different setups of AGC are compared and a feedforward (FF) approach is developed for lateral asymmetries of the entry thickness profile. Simulation studies based on a validated mill stand model demonstrate the benefit of combining AGC with a feedforward controller to compensate for asymmetries.

Parameter Identification and Control Scheme for Monitoring Automatic Thickness Control System with Measurement Delay

The thickness of the steel strip is an important indicator of the overall strip quality. Deviations in thickness are primarily controlled using the automatic gauge control (AGC) system of each rolling stand. At the last stand, the monitoring AGC system is usually used, where the deviations in thickness can be directly measured by the X-ray thickness gauge device and used as the input to the AGC system. However, due to the physical distance between the thickness detection device and the rolling stand, time delay is unavoidably present in the thickness control loop, which can affect control performance and lead to system oscillations. Furthermore, the parameters of the system can change due to perturbations from external disturbances. Therefore, this paper proposes an identification and control scheme for monitoring AGC system that can handle time delay and parameter uncertainty. The cross-correlation function is used to estimate the time delay of the system, while the system parameters are identified using a recursive least squares method. The time delay and parameter estimates are then further refined using the Levenberg-Marquardt algorithm, so as to provide the most accurate parameter estimates for the complete system. Simulation results show that, compared with the standard Proportion Integration Differentiation (PID) controller approach, the proposed approach is not affected by changes in the time delay and parameter uncertainties.

Iterative Learning Control with an Improved Internal Model for a Monitoring Automatic-Gauge-Control System

The long time delay in the monitoring automatic gauge control (AGC) of strip rolling by a tandem hot mill adversely affects system stability. To solve this problem, internal model control (IMC) and iterative learning control were applied to a monitoring-AGC system. A mathematical model of the hydraulic gap control system was established focusing on the seventh stand of a 1450-mm tandem hot mill in a factory. Model parameters were identified employing a particle swarm optimization algorithm. Using the identified hydraulic gap control model, a monitoring AGC system with an improved internal model (IIMC-MNAGC) and an iterative-learning-control strategy for an improved-internal-model monitoring AGC system (ILC-IIMC-MNAGC) were established. Finally, simulation experiments for IIMC-MNAGC and ILC-IIMC-MNAGC were conducted using MATLAB/Simulink software. The simulation results show that for the IIMC-MNAGC system, when the model matches, the rising time reaches 43.6 msec, the overshot reaches 4.34%, the integral square error (ISE) reaches 0.0131, and the Hα norm reaches 2.953. These levels are acceptable for the MN-AGC system. When there is model mismatch due to the inaccuracy of the pure delay, for the IIMC-MNAGC system, the rising time increases to 263.5 msec and the overshot increases to 36.7%, which are unacceptable for the monitoring AGC system. When there is model mismatch for the ILC-IIMC-MNAGC system, the rising time reaches 38.9 msec, the overshot reaches 1.37%, the ISE reaches 0.0095, and the Hα norm reaches 2.989. These levels are acceptable for the monitoring AGC system.

Modeling and Extended State Observer Based Dynamic Surface Control for Cold Rolling Mill System

The modeling and control problems are investigated for cold rolling mill system. Firstly, we establish a monitor automatic gauge control (MAGC) model for a practical cold rolling mill system. The new model is with mismatched uncertainties. Then, an extended state observer (ESO) is developed to estimate uncertainties. In the general high-order systems, the ESO is also used to estimate states. By dynamic surface control method, we design the controller to guarantee stabilization of the cold rolling mill system. Furthermore, we extend proposed method to general high-order systems, in which we analyze the difference from cold rolling mill system. Finally, simulation results for MAGC system are presented to demonstrate the effectiveness of the proposed control strategy.

Sliding mode variable structure control for smith prediction monitoring AGC system based on double power reaching law

To overcome unfavorable influence of the large time delay existing in monitoring automatic gauge control (AGC) of tandem hot mill and model mismatching greatly on strip rolling process on system stability, a sliding mode variable structure control for Smith prediction monitoring AGC system based on double power reaching law was designed. The mathematical model of the hydraulic gap control (HGC) system was established based on the 7# stand in 1450 mm tandem hot mill of a factory and model parameters were identified by Levy curve fitting method. Based on the identified model, conventional Smith prediction monitoring AGC system (SP-MNAGC), sliding mode variable structure control for Smith prediction monitoring AGC system based on constant rate reaching law (CR-SPSMC-MNAGC) and sliding mode variable structure control for Smith prediction monitoring AGC system based on double power reaching law (DP-SPSMC-MNAGC) were researched with Matlab/Simulink software. The results show that the three different controllers acquire good control effect during model matching. But during model mismatching, for SP-MNAGC system, the maximum value of rising time will increase to 2102.3 ms, the overshot will increase to 39.6 %; for CR-SPSMC-MNAGC system, the maximum value of rising time will increase to 348.3 ms, the overshot will increase to 13.1 %; for DP-SPSMC-MNAGC system, the overshot is less than 8.7 %, and the rising time is less than 36.1 ms in any case. Besides this, DP-SPSMC-MNAGC system can weaken the chattering of sliding mode effectively.

Improvement of Algorithms for Automatic Gauge Control System of the Hot-Rolling Mill

The paper studies issues of improvement of the automatic gauge control system (AGCS) in the continuous hot-strip train. The factors influencing longitudinal strip gauge deviations have been classified. It has been proved that Davy McKee AGCS installed at the 2,000 mill of OJSC Magnitogorsk Iron and Steel Works (OAO MMK) does not provide control accuracy factors required at the light gauge strip rolling. The paper considers the functional chart of the improved AGCS realizing algorithm of the dynamic gauge correction. Experimental studies confirm that the developed chart helps to decrease longitudinal strip gauge deviations and, hence – to improve the quality of the products.

Modelling and Analysis of Step Response Test for Hydraulic Automatic Gauge Control

The step response for hydraulic automatic gauge control (HAGC) determines the steel rolling speed and the steel sheet thickness in the process of rolling production. In this paper, the step response test process of HAGC was analysed, and a test approach was proposed for it. Based on that, the transfer function model of the step response test was established and simulated by using Matlab. In order to reduce the settling time and the overshoot, an adaptive proportional-integral-derivative (APID) link was presented in order to compensate for the input signal by using back propagation neural networks (BPNN). The experimental results show that the improved step response test model reaches the process requirements of HAGC, eliminates the jitter of the HAGC system at the start-up phase, and has better stability as well as faster response for steel sheet rolling.

Discrete-time Explicit Model Predictive Control for Gauge-Looper Integrated System in Hot Strip Finishing Mill

The development of an innovative discrete-time EMPC (Explicit Model Predictive Control) strategy based on multi-parametric quadratic program is traced for the gauge-looper integrated control in HSFM (Hot Strip Finishing Mill). Controller design is based on the linearized model of the integration of downstream AGC (Automatic Gauge Control) sys- tem and upstream looper-tension system. The proposed EMPC strategy gives an explicit piecewise affine control law which greatly reduces the on-line computational burden. Discrete-time EMPC achieves better performance by coordina- tion control and is more suitable for implementation on PLC (Programmable Logic Controller) compared with conven- tional controllers. Experiment results verify the effectiveness of the proposed strategy.

Research and Application of Thickness Control Strategies in Steel Plate Rolling

Thickness accuracy of plate production depends on Automatic Gauge Control (AGC) in the plate mill area. A typical modern thickness control system design and implementation of a steel plate mill is discussed together with the im- pact on the design of process models, available measurements, available control actuators and material properties. A high- level software design approach provides the ability to make quick and accurate modifications to both control loops and tuning constants. Control loop strategies and theoretical concepts of steel plate rolling are discussed. Performance results achieved during the startup of a steel plate mill are included.

The Performance Testing System of Force Motor Valve

Hitachi force motor valve has been widely used in the hydraulic automatic gauge control (AGC) system of rolling mill due to the characteristics of fast response, high control accuracy and strong anti-pollution ability. It is an important part to control the steel production cost by detecting the performance index of the FMV effectively and in real time. Traditional Servo valve test system detects its static characteristics through the flow and pressure changes between the traffic cavity, and this principle can solve the three position four way servo valve performance test. However, FMV is a special three-way valve and it is hard to test its static characteristic curve like three position four way servo valve. This paper proposes a FMV testing method and has realized it. The test platform is designed and built according to the hydraulic valve testing performance index for detecting the performance of a force motor valve. Not only were force motor valve (FMV) performance characteristics tested effectively but also the performance curves were drawn. The results show that the FMV performance testing method we have built can be effectively used to detect the static performance index of FMV.

Improved Smith prediction monitoring AGC system based on feedback-assisted iterative learning control

The performance of Smith prediction monitoring automatic gauge control (AGC) system is influenced by model mismatching greatly in strip rolling process. Aiming at this problem, a feedback-assisted iterative learning control strategy, which learned unknown modeling error by using previous control information repeatedly, was introduced into Smith prediction monitoring AGC system. Firstly, conventional Smith predictor and improved Smith predictor with PI-P controller were analyzed. Secondly, on the basis of establishing of feedback-assisted iterative learning control strategy for improved Smith predictor, process control signal update law and control error were deduced, then convergence condition of this strategy was put forward and proved. Finally, after modeling the automatic position control system, the PI-P Smith prediction monitoring AGC system with feedback-assisted iterative learning control was researched through simulation. Simulation results indicate that this system remains stable during model mismatching. The robustness and response of monitoring AGC is improved by development of feedback-assisted iterative learning control strategy for PI-P Smith predictor.

Sliding Mode Control of Strip Rolling Mill Hydraulic AGC System

Hydraulic automatic gauge control (AGC) is a very important part of rolling mill for magnesium plate rolling. The control effect of automatic gauge control system influences the quality of the rolled product directly. AGC system is an essentially nonlinear, time delay, time-varying, large inertia, multivariable and coupling complex system, which increase the designing difficulty of control system. Based on the mathematical model of the automatic gauge control system, a simulation platform of rolling mill is set up, and a sliding mode variable structure controller is designed to realize position control for the hydraulic automatic gauge control system. The control effect of the proposed sliding mode controller is compared with that of a general PID controller whose parameters was adjusted by ZieglerNichols method. Simulation results show that the sliding mode controller has strong antiinterference ability and can give satisfactory control effect.