Hydraulic Gap Control Research Articles

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.

Hydraulic gap control of rolling mill based on self-tuning fuzzy PID

Hydraulic gap control of rolling mill based on self-tuning fuzzy PID

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.

Improvement of Electric and Mechanical System for Automated Strip Tension Control at Continuous Wide-Strip Hot-Rolling Mill

It is known that a modern trend in development of wide-strip hot-rolling mill technologies is gauge diversification owing to production of thin strip. Engineers are mastering methods of rolling 0.8−1.5mm strip that was earlier manufactured at cold rolling mills only. Tension in inter-stand gaps of the continuous train is found to influence thin strip gauge greatly. Based on the example of the 2,500mm mill at OJSC Magnitogorsk Iron and Steel Works, it has been proven that existing tension and loop size indirect control systems (TLSCSs) does not meet increasingly stringent requirements for accuracy of tension control. Here, improvement of control algorithms does not result in a significant quality rise. Thus, capabilities of the high-speed system for automated gauge control based on the Hydraulic Gap Control (HGC) may be useful. The improved TLSCS has been developed that enables control of the roll speed and HGC location of the previous stand. The system provides improvement of dynamic data due to compensation of the impact of the loop gear location of tension. Mathematical modeling has proven that the system developed ensures control of specific tension to a tolerance of ±10%. A dynamic component of the strip gauge deviation is within 3%. The TLSCS developed is recommended for implementation at 2,500mm mill of OJSC Magnitogorsk Iron and Steel Works within the framework of the current reconstruction.

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.

Identification and optimization for hydraulic roll gap control in strip rolling mill

In order to improve the control performance of strip rolling mill, theoretical model of the hydraulic gap control (HGC) system was established. HGC system offline identification scheme was designed for a tandem cold strip mill, the system model parameters were identified by ARX model, and the identified model was verified. Taking the offline identified parameters as the initial values, online identification using recursive least square was carried out with model parameters changing. For the purpose of improving system robustness and decreasing the sensitivity due to model errors, the HGC system based on generalized predictive control (GPC) was designed, and simulation experiments for traditional controller and GPC controller were conducted. The results show that both controllers acquire good control effect with model matching. When the model mismatches, for the traditional controller, the overshot will increase to 76.7% and the rising time will increase to 165.7 ms, which cannot be accepted by HGC system; for the GPC controller, the overshot is less than 8.5%, and the rising time is less than 26 ms in any case.

Influence of Internal Leakage in Hydraulic Capsules on Dynamic Behavior of Hydraulic Gap Control System

In hot rolling mills the plastic deformation of the strip is realized at high force and plastic strain speed controlled by electro-hydraulic servo actuators. These hydraulic servo actuators - hydraulic capsules – are capable to adjust the rolling gap at great rolling force dynamically. The dynamic behaviour of the rolling mill’s AGC (automatic gap adjustment) system mainly depends on the correct operation of hydraulic actuators and servo valves. These equipments are great value, planned maintenance is essential for reliable correct operation. The maintenance includes the refurbish of damaged, worn surfaces inside the cylinder and replacement of worn out seals. In the study a laboratory hydraulic positioning system was used to examine the effect of hydraulic actuator internal leakage to dynamic behaviors of the positioning system. Because the laboratory test system is similar to the hydraulic gap adjustment system therefore the laboratory test results can be extended to the rolling mill’s Hydraulic Gap Control system.

A Framework for Adaptive Online Thickness Control at Plate Mill of Bhilai Steel Plant

The Plate Mill at Bhilai Steel Plant (BSP) has two reversing stands, one functioning as the roughing mill, and the other as the finishing mill. The nominal thickness of the slab is 245 mm, which is reduced to about 40 mm as thick plates in the roughing mill and the thinner plates are processed further in the finishing mill. The Plate Mill is now undergoing a major revamp with the main component being the hydraulic automation gap control (HAGC) and the supporting automation systems. The HAGC is backed up by proper sensors, instrumentation, microprocessor-based control equipment working in real time. The installation of the HAGC provides for controlling thickness variations due to process variables like plate temperature, mill spring, and so on. Mathematical models for both off-line simulation and adaptive mill setup have been developed indigenously for automatic control of plate thickness in the revamped Plate Mill. The control of thickness of the plate from head to tail is envisaged as a two-step process, viz., (i) a Level II Adaptive Algorithm, where an optimum drafting schedule generated “on the fly” is downloaded as reference points for the Level 1 automation and (ii) a Level 1 Feedback Controller for applying the necessary correction in the roll gap, for process deviations during rolling. The off-line mathematical models have been validated with extensive data collected from the mill. Once they are implemented online, it is anticipated that continuous updating will improve its performance and will reach international levels of performance guarantee.

Modeling and Simulation of Hydraulic Gap Control System in a Hot Strip Mill.

Hot strips are presently being rolled out with considerable thickness accuracy. This has been made possible due to superordinated control system comprising of adaptive setup model, monitor thickness control, automatic gauge control, tension and looper control, hydraulic gap control etc. The present work is, however, confined to modeling and simulation studies of hydraulic gap control system in the last stand of the finishig mill of a typical hot strip mill (HSM). The simulation results based on the model show that the system operates effectively to provide high thickness accuracy and good response behavior.