Automatic Gauge Control System Research Articles

Stability and stabilization for the hydraulic automatic gauge control system of cold rolling mill with time delay and saturation

This paper studies the stability and stabilization of hydraulic automatic gauge control(HAGC) systems with time-varying delay and actuator saturation. First, a mathematical model of HAGC systems is established considering the measurement delay and saturation factors. With the help of state transformation, the measurement delay is transformed into input delay and the generalized sector condition is adopted to deal with the saturation problem in HAGC systems. Then, a new augmented L-K functional is constructed to contain more delay information to reduce the conservativeness of the stability criteria. Furthermore, by combining the proposed L-K functional with some advanced inequalities, the stability conditions and controller are derived with the aid of linear matrix inequalities(LMIs). Finally, the effectiveness of the proposed control algorithm is verified by simulation results.

Rolling force and length of strip head and tail sections under unsteady deformation conditions

This paper describes the results of an experimental study that looked at the distribution of strains and rolling forces along the length of brass (L63), bronze (BrOF6,5-0,23) and copper (M3, M0) strips in a 150×235 twin rolling mill equipped with a microcontroller-based high-precision roll load measurement system. 2 and 3 mm thick workpieces with the widths of 10, 20 and 30 mm and the length of about 200 mm taken from the commercial batches of rolled copper, brass and bronze were used for the study. The workpieces were rolled at the Kolchugino and Kirov Non-Ferrous Metals Processing Plants. The reduction rate was varied within the range of 4 to 45%. The paper contains graphs showing the distribution of rolling forces along the strip length. The graphs indicate that the length of the strip head and tail sections, which experience unsteady rolling conditions, is dictated by the reduction degree, mechanical properties and dimensions of the strip. It was found that the length of the strip head and tail sections undergoing unsteady deformation tends to increase as the reduction rate increases. It was established that the initial mechanical properties of the strips had a significant effect on the unstable rolling duration and the length of the strip head and tail sections deviating from the given dimensions of the proper strip. Regression equations were obtained that can help predict the duration of unsteady rolling conditions with regard to copper strips as a function of their initial rigidity and reduction. The results of the study can be useful when finetuning rolling mills, as well as automatic gauge control systems, to ensure strips are rolled to precision along their entire length.

Roll eccentricity extraction and compensation based on MPSO-WTD and ITD.

To meet the high thickness accuracy requirements in cold-rolling processes, a roll eccentricity signal extraction method based on modified particle swarm optimization and wavelet threshold denoising (MPSO-WTD) with intrinsic time-scale decomposition (ITD) is proposed. The strong denoising ability of the wavelet is combined with the decomposition and recognition attributes of ITD for non-stationary signals. Periodic disturbances in strip thickness caused by roll eccentricity are actively compensated. First, the wavelet is used to denoise the signal and the MPSO algorithm is applied to determine a rational threshold and improve the calculation efficiency. Then, the denoised signal is decomposed into proper rotational components (PRCs) using the ITD method, and an appropriate PRC component representing the eccentricity signal is extracted. Finally, the eccentricity compensation signal is applied in the automatic gauge control (AGC) system of the cold rolling mill. During the rolling process, the rolling speed is not constant and will directly affect the frequency of the roll eccentricity signal. To solve this problem, an encoder is installed at the end of the roll and the compensation frequency of the roller eccentricity signal is determined in the roller eccentricity compensation system according to the pulse number output. The results of simulations and experiments show that roll eccentricity signals extracted using the proposed method can effectively remove the influence of interference signals. An average improvement of 62.3% in the roll eccentricity compensation effect was achieved under the stable rolling condition in the finishing rolling stage.

Advancement of Roll-Gap Control to Curb the Camber in Heavy-Plate Rolling Mills

The quality of steelwork products depends on the geometric precision of flat products. Heavy-plate rolling mills produce plates for large-diameter pipes and for use in shipbuilding, mechanical engineering, and construction. This is why the precision requirements are so stringent. Today’s Mills 5000 produce flat products of up to 5 m in width; the operation of these units shows ‘camber’ defects and axial shift of the roll at the stand exit point. This induces greater loss of metal due to edge trimming and involves a higher risk of accidents. These defects mainly occur due to the asymmetry in the roll gap, which is in turn caused by their misalignment in rolling. As a result, the feed varies in gauge, and the strip moves unevenly. The paper’s key contribution consists in theoretical and experimental substantiation and development of a set of control methods intended to address roll-gap asymmetry. The methods effectively compensate for the asymmetry resulting from the “inherited” wedge, which preexists before the strip enters the stand. They also compensate for the “ongoing” roll misalignment that is caused by the difference in force on the opposite side of the stand during rolling. This comprehensive approach to addressing camber and axial displacement of the feed has not been found in other sources. This paper presents a RAC controller connection diagram that ensures that the roll gap is even across the feed. The paper notes the shortcomings of the design configuration of the controller and shows how it could be improved. The authors have developed a predictive roll-gap asymmetry adjustment method that compensates for the deviations in gauge during the inter-passage pauses. They have also developed a method to control gap misalignment during rolling. The paper showcases the feasibility of a proportional-derivative RAC. The methods have been tested by mathematical modeling and experimentally. The paper further shows oscillograms sampled at Mill 5000 after implementing the developed solutions. Tests confirm far better precision of the screw-down mechanisms on the opposite sides of the stand. This reduces the variation in gauge across the feed and thus curbs the camber defect. As a result, the geometry of the flat improves, and less metal is lost in trimming. The paper further discusses how the RAC controller interacts with the automatic gauge control system. The conclusion is that these systems do not interfere with each other. The developed systems have proceeded to pilot testing.

Instability Condition Derivation for Hydraulic AGC System under Pressure Closed-Loop Control

In strip rolling, hydraulic automatic gauge control (HAGC) system is the key element to guarantee the precision of strip gauge. The stability of the kernel pressure closed loop (PCL) in the HAGC system plays an essential role in guaranteeing the rolling process with high performance. Nevertheless, there is some difficulty in exploring the instability mechanism of the HAGC system due to the fact that the PCL is a representative nonlinear closed-loop control system. In this work, for each component of the HAGC system, the mathematical model was established. And on the basis of the linking relation of various elements, we derived the incremental transfer model of the PCL system. Furthermore, in accordance with the deduced information transfer relation, the transfer block diagram of disturbing variable of the PCL system was obtained. Moreover, for the purpose of deriving the instability condition of the PCL system, the Popov frequency criterion was employed. The instability conditions of the HAGC system were obtained under PCL control. Furthermore, the derived instability conditions of the HAGC system were experimentally verified under various working conditions. The research results provide a fundamental foundation for studying the instability mechanism of the HAGC system.

Parameter identification method of hydraulic automatic gauge control system based on chaotic wolf pack optimization algorithm

In the metallurgical industry, the hydraulic automatic gauge control (HAGC) system is a kernel system used to assure the thickness precision of a rolling piece. In addition, the HAGC system is a complex nonlinear system with multiple degrees of freedom (DOF). It is difficult to identify the key parameters and obtain an accurate prediction model that can reflect the output performance of the HAGC system. On the basis of theoretical analysis, a vertical vibration model of the HAGC system with two DOF was established. Moreover, based on the swarm intelligence in nature, a novel method for model parameter identification of the HAGC system was explored, and a parameter identification method was proposed based on the chaotic wolf pack optimization algorithm. Furthermore, the proposed method was verified by experiments. The results indicate that the proposed method presents laudable identification ability. The theoretically predicted response of the identification model is consistent with the measured response of the actual system. The error of the response output waveform is small. The proposed method can be used to identify key structural parameters of the HAGC system.

Distributed Consensus Control for Automatic Gauge Control of Hot Strip Mills

In this study, the distributed control strategy is proposed for the automatic gauge control(AGC) system, which is a typical multi-agent system. The distributed control protocol is developed with the subspace identification method using the measurements of the local agent and its neighbors directly, without any knowledge of the AGC system dynamics. The stability analysis of the multi-agent system with the proposed control protocol is given. In addition, the consensus control protocol with communication time delay is investigated. Finally, simulation results are carried out to verify the feasibility and effectiveness of the proposed control strategy.

Разработка цифровых алгоритмов управления приводами мехатронной системы реверсивной клети толстолистового прокатного стана

Expanding the plate mill product range implies the improvement of control algorithms for the mechatronics control system drives of the reversing stands. The most important objectives include increasing the accuracy of geometric dimensioning and tolerancing, as well as improving the profile and surface flatness of rolled pro­ducts. The structure explaining the automatic ROLL-GAP CONTROL concept is provided, which allows controlling the thickness and gap between SMS-Demag AG rolls. This concept is implemented in the '5000' mill stand of Magnitogorsk Iron and Steel Works. The structural diagram of the automatic gauge control system (AGS) is presented. The functional diagram of the hydraulic gap control (HGC) system is presented, which includes a fast proportional control channel and a relatively slow integral position control channel. The principle of automatic thickness control is discussed, implemented in the automatic gauge control (AGC) system of the mill stand TCS controller. The diagram and dependences are prepared for the calculation of the nonlinear thickness controller parameters. The functions of the RAC regulator are described, intended for compensation of the tensile difference (gap spacing) at the mill stand sides. The dynamic impact compensation system functions are considered. The removal of the roll bending and deformation control signals is substantiated. The disadvantages of AGC are noted for sheets with a thickness below 10 mm. The most dangerous case is the tearing of metal fragments from the rear sheet side caused by the incorrect operation of the gauge control system. A method for hydraulic gap control is proposed based on the fast increase of the roll gap in the rear part of the rolled sheet during the last passage when rolling thin sheets. The results of experimental studies made on the '5000' mill are presented. The efficiency of the proposed control method has been confirmed. The oscillograms of signals are presented characterizing thickness variations. HGC and AGC systems with the proposed adjustments are proven to provide high-accuracy hydraulic position control and thickness control along the sheet length and width.

Simulation Model of Cold Rolling Mill

This work deals with the simulation model of multi-machines system as cold rolling mill is considered as application. Drivers of rolling system are a set of DC motors, which have extend applications in factories as aluminum rolling. Interconnection of multi DC motors in such a way that they are synchronized in their rotational speed. In cold rolling, the accuracy of the strip exit thickness is a very important factors. To realize accuracy in the strip exit thickness, Automatic Gauge Control system is used. In this paper MATLAB/SIMULINK models are proposed and implemented for the entire structures. Simulation results were presented to verify proposed model of cold rolling mill

Discrete Model Predictive Control Scheme for an Integrated Gauge-Looper Control System in a Tandem Hot Strip Mill

There exists strong coupling and a complex multivariable relation among the strip gauge, looper angle and strip tension in tandem hot rolling. To improve the gauge precision of the hot strip, the dynamic relationship among these three variables must be determined. In this paper, a new coordinated optimal control scheme based on discrete model predictive control (DMPC) theory was presented for an automatic gauge control and looper control (AGC-LP) integrated system. First, a state-space model of the AGC-LP integrated system was established based on a 1700 mm tandem hot strip mill. Then, to achieve the desired dynamic performance with the AGC-LP integrated system, a performance index function and an optimal control sequence were designed for the DMPC controller. The simulation results showed that the proposed DMPC controller had better robustness and adaptability to modeling uncertainties and external disturbances than a traditional proportional-integral (PI) controller.

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.

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.

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.

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.

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.