MILL CONTROL SYSTEM AND METHOD FOR CONTROL OF METAL STRIP ROLLING

Mill control system and method for metal strip rolling controlled in response to a sequence of controller scans are provided. A sensor suite is coupled to sense a plurality of parameters regarding the strip rolling. A model responsive to the sensed parameters is configured to estimate per scan at least one matrix based on the sensed parameters and indicative of state conditions of the strip rolling. A controller includes an inner control loop configured to effect a control law to generate a control vector per scan. The inner control loop may be configured to have dynamic characteristics, which remain the same for each scan of the controller. The dynamic characteristics of the inner control loop are effective to determine an online control solution based on the matrix indicative of the state conditions of the strip rolling, without having to compute a Riccati control solution per scan

POINTWISE LINEAR QUADRATIC OPTIMAL CONTROL OF A TANDEM COLD ROLLING MILL

ABSTRACTPOINTWISE LINEAR QUADRATIC OPTIMAL CONTROL OF ATANDEM COLD ROLLING MILLJohn R. Pittner, PhDUniversity of Pittsburgh, 2006The tandem cold rolling of metal strip is a complex multivariable process whose control presents a significant engineering challenge. The present technology generally relies on a control structure wherein the interactive coupling between process variables is partially reduced by several single-input-single-output and single-input-multi-output control loops operating on certain variables to decompose the overall problem into several separate problems to attempt to allow independent adjustment of strip tension and thickness anywhere in the mill. However, while the existing systems generally have been successful in producing an acceptable product, their failure to completely counteract the effects of interactions between process variables has limited their capability for improvement in performance and in robustness to disturbances and uncertainties. Various techniques for improvement have been proposed and some have been implemented. Many of these techniques offer some improvements, but also have shortcomings. Therefore there is a need for a better approach. It is considered that the pointwise linear quadratic optimal control might fulfill this need. This dissertation investigates the theoretical and applied aspects of this technique for control of a tandem cold rolling mill using criteria based on practical applications. A mathematical model of the mill is developed from which nonlinear state space equations are derived. Using these equations, a pointwise linear quadratic optimal controller is developed, and its performance for variations in operating speed and product are confirmed by simulation. Robustness to disturbances and uncertainties is also confirmed by simulation. The results are compared with those using typical industry practice

Stimulation of specific GTPase activity by vasopressin in isolated membranes from cultured rat hepatocytes

AbstractMembranes were isolated by isotonic homogenization and differential centrifugation from rat hepatocytes cultured overnight. The specific GTPase activity of the membranes was 1–1.3 pmol γ-labelled GTP hydrolysed/mg protein per min in the presence of 1.2 mM Na+, 2 mM EGTA, 1 mM ATP and 0.2 mM 5-adenylyl imidodiphosphate. Under these conditions there was a stimulation of specific GTPase activity of no more than 20% by 11–115 nM vasopressin. No effect of vasopressin was seen in the presence of 1.7 μM free Ca2+ or 100 mM Na+. The findings indicate that vasopressin is able to influence GTPase activity as well as accelerate phosphoinositide breakdown in rat hepatocytes

Controller for improving the quality of the tandem rolling of hot metal strip

The tandem hot metal strip rolling process presents a difficult control challenge because of its highly complex and nonlinear nature. This challenge is heightened by the hostile hot metal rolling environment which precludes the location of certain sensors to measure variables that are important for control. Based on our previous work using a state-dependent Riccati equation technique for development of a controller for the tandem cold metal rolling process, it is considered that a similar basis could be expanded upon to realize an improved method for the control of this more complex application. In this paper we present a comprehensive model of this process plus the results of our first efforts in the development of a suitable controller, which for control of this application is different than previous methods. The results of simulations of the controller coupled to the model show a strong potential for improvement in the quality of the final product. © 2010 AACC

Conventional Control

This chapter presents an overall view of conventional control concepts for the tandem cold metal rolling process to serve as a background for the chapters which follow on advanced control. While the emphasis is on automatic control of strip thickness and interstand tension, the control of the process in the areas of eccentricity compensation, strip flatness, and threading of the mill also is briefly addressed. Included in each area are examples of typical control techniques, most of which are taken from actual industry applications

Advanced Control To Reduce The Likelihood Of Cobbles In The Tandem Rolling Of Hot Metal Strip

The performance of our state-dependent Riccati equation-based controller in the face of various extended uncertainties and disturbances was shown in our previous work to be highly successful. In our previous investigation, we have taken the material of the workpiece to be of one phase (austenite) and of medium and low carbon equivalents. However, it is recognized that a disturbance such as a greater decrease in temperature while processing a material of extra-low carbon equivalent could result in a change in the phase of the workpiece. Such a change in phase can result in a wreck (a cobble) in the mill, with resulting downtime and the possibility of equipment damage. In this paper, we expand our previous work to examine the effects of changes in the temperature of a workpiece of extra-low carbon equivalent and show that any resulting changes in the phase of the workpiece are effectively handled by our controller to reduce the likelihood of cobbles in the mill

Process Model

This chapter presents a mathematical model suitable for the development of a controller for the tandem cold metal rolling process. A comprehensive model is developed and put into the form of state and output equations. The model is verified by simulation, the results of which are compared to the results of simulations based on a model that is recognized as a benchmark standard for verification

Control Of The Tandem Hot Strip Mill Under Expanded Uncertainties And Disturbances

Previously it has been shown that a controller based on the use of the state-dependent Riccati equation (SDRE) technique has resulted in significant improvements in performance. In our previous work controller performance under certain disturbances and uncertainties that are considered typical for tandem hot rolling was addressed. While the performance under these conditions was quite successful, performance under an expanded set of conditions remained to be evaluated. In this paper we examine performance under such a set of disturbances and uncertainties and show that the improvement in controller performance is retained under these expanded operational aspects. This improves the confidence in the performance of the previously developed controller under these conditions. © 2013 IEEE

Improvement In Control Of The Tandem Hot Strip Mill

Our previous work has shown that the use of the state-dependent Riccati equation (SDRE) technique as a basis for the development of a suitable controller for the tandem hot metal rolling process has resulted in significant improvements in performance. However, the method of setting the controller parameters was left as a part of future efforts. In this paper, we show that improvements in the implementation of the SDRE method provide a method of easily setting initial control parameters and then making automatic adjustments to the controller as the strip is processed through the mill. This eliminates the need for an online solution of the SDRE or the need for lookup tables to make controller settings. These improvements greatly simplify the design and implementation of the controller and also make the SDRE technique even more attractive in the control of many similar complex industrial processes. © 1972-2012 IEEE