Robust shape control in a sendzimir cold-rolling steel mill

The shape control problem for a Sendzimir 20-roll cold rolling steel mill is characterised by operation over a wide range of conditions arising from roll changes, changes in rolling schedules and changes in material gauge, width and hardness. Previous approaches to the problem suggest storing a large number of precompensator matrices to cater for the full range of operating conditions. This paper, on the other hand, attempts to synthesise a controller which is optimally robust to changes in the conditions associated with the rolling cluster, resulting in a reduced storage requirement for the controlling computer. The performance of the robust controller is evaluated via nonlinear simulation

An optimal output feedback solution to the strip shape multivariable control problem

The design of shape control systems for producing flat metal strip products is discussed. Static and dynamic models for a Sendzimir mill are described briefly. Optimal dynamic output feedback solutions are presented for the shape control system design. The optimal control solutions provide guidance on the best structure to be used for shape control. It is shown that by judicious choice of the performance criterion weighting matrices particularly simple controllers may be derived; dimension reduction by parameterisation is also shown to result in a simplification to the controller structure. The effect of nonlinearities in the actuators is discussed, a linear approximation being used for design purposes. A variety of simulation results are presented showing the transient response and the shape control performance of the multivariable system. The effect of mismatch is also demonstrated, that is, using the controller for a mill schedule other than the one for which it was designed

An optimal output feedback solution to the strip shape multivariable control problem

The design of shape control systems for producing flat metal strip products is discussed. Static and dynamic models for a Sendzimir mill are described briefly. Optimal dynamic output feedback solutions are presented for the shape control system design. The optimal control solutions provide guidance on the best structure to be used for shape control. It is shown that by judicious choice of the performance criterion weighting matrices particularly simple controllers may be derived; dimension reduction by parameterisation is also shown to result in a simplification to the controller structure. The effect of nonlinearities in the actuators is discussed, a linear approximation being used for design purposes. A variety of simulation results are presented showing the transient response and the shape control performance of the multivariable system. The effect of mismatch is also demonstrated, that is, using the controller for a mill schedule other than the one for which it was designed

Diagonalisation of a class of multivariable system via an actuator linearisation technique

Many multivariable (systems with many inputs/outputs) industrial processes can, to a good degree of approximation, be modelled by a transfer function matrix, where all of the interaction occurs in a matrix of constant coefficients. This reflects the fact that the dynamics of the section in which the interaction occurs are very fast compared with the other dynamics in the system. Examples of such systems include steel rolling mills and boiler systems. Such multivariable systems are relatively easy to design controllers for, since the system may be diagonalised by an inverse of the constant gain matrix, followed by suitable single-loop dynamic compensation. However, this approach depends on the linearity of the dynamical elements in the system. Such a condition is voilated by the presence of non-linear actuators, which are a feature of many industrial systems. The presence of such actuators within a multivariable control system as described above can cause very significant interaction problems, with associated degradation in performance, particularly during transients. This paper describes a straightforward technique, which is effective in linearising typical non-linear industrial actuators, allowing diagonalisation to be effectively achieved at all frequencies. The technique relies on a simple describing function analysis and manifests itself as a time-varying linearising precompensator for each non-linear actuator. A simple example is used to demonstrate the effectiveness of the method and it is then shown in application with multivariable boiler and steel mill models

Smart Manufacturing in Rolling Process Based on Thermal Safety Monitoring by Fiber Optics Sensors Equipping Mill Bearings

The steel rolling process is critical for safety and maintenance because of loading and thermal operating conditions. Machinery condition monitoring (MCM) increases the system’s safety, preventing the risk of fire, failure, and rupture. Equipping the mill bearings with sensors allows monitoring of the system in service and controls the heating of mill components. Fiber optic sensors detect loading condition, vibration, and irregular heating. In several systems, access to machinery is rather limited. Therefore, this paper preliminarily investigates how fiber optics can be effectively embedded within the mill cage to set up a smart manufacturing system. The fiber Bragg gratings (FBG) technology allows embedding sensors inside the pins of backup bearings and performing some prognosis and diagnosis activities. The study starts from the rolling mill layout and defines its accessibility, considering some real industrial cases. Testing of an FBG sensor prototype checks thermal monitoring capability inside a closed cavity, obtained on the surface of either the fixed pin of the backup bearing or the stator surrounding the outer ring. Results encourage the development of the whole prototype of the MCM system to be tested on a real mill cage in full operation

A static model of a Sendzimir mill for use in shape control.

The design of shape control systems is an area of current interest in the steel industry. Shape is defined as the internal stress distribution resulting from a transverse variation in the reduction of the strip thickness. The object of shape control is to adjust the mill so that the rolled strip is free from internal stresses. Both static and dynamic models of the mill are required for the control system design.The subject of this thesis is the static model of the Sendzimir cold rolling mill, which is a 1-2-3-4 type cluster mill. The static model derived enables shape profiles to be calculated for a given set of actuator positions, and is used to generate the steady state mill gains. The method of calculation of these shape profiles is discussed. The shape profiles obtained for different mill schedules are plotted against the distance across the strip. The corresponding mill gains are calculated and these relate the shape changes to the actuator changes. These mill gains are presented in the form of a square matrix, obtained by measuring shape at eight points across the strip

An investigation into the design and performance of an automatic shape control system for a Sendzimir cold rolling mill.

Shape (or flatness) control for rolled steel strip is becoming increasingly important as customer requirements become more stringent. Automatic shape control is now more or less mandatory on all new four-high cold mills, but no comprehensive scheme yet exists on a Sendzimir mill. This is due to the complexity of the control system design on such a mill, where many more degrees of freedom for control exist than is the case with the four-high mills.The objective of the current work is to develop, from first principles, such a system; including automatic control of the As-U-Roll and first intermediate roll actuators in response to the measured strip shape. This thesis concerns itself primarily with the As-U-Roll control system. The material presented is extremely wide-ranging. Areas covered include the development of original static and dynamic mathematical models of the mill systems, and testing of the plant by data-logging to tune these models. A basic control system philosophy proposed by other workers is modified and developed to suit the practical system requirements and the data provided by the models. The control strategy is tested by comprehensive multivariable simulation studies. Finally, details are given of the practical problems faced when installing the system on the plant. These include problems of manual control inter-action bumpless transfer and integral desaturation.At the time of presentation of the thesis, system commissioning is still in progress and production results are therefore not yet available. Nevertheless, the simulation studies predict a successful outcome, although performance is expected to be limited until the first intermediate roll actuators are eventually included in the scheme also

Computer applications in steel industry

An overview of the current status of computer applicat-ions in the steel industry has been presented from the point of view of process automation and control. Specific areas covered range from sintering to rolling - including energy and transport management. It has been concluded that development of more intelligent man-machine interface for computer aided analysis, simulation and implementation of control system coupled with advances in software engi-neering, parallel processing, high performance graphics and artificial intelligence based systems have led to cons-iderable advancement in all areas as evidenced by signi-ficant improvement in both the plant productivity and pro-duct quality, the world over. Efforts being made in India in general and at R&D Centre of SAIL in particular have been highlighted. In this context, generation of our own technology and a rational and intelligent selection and adoption of various technical advances has been emphasised

Effects of rolling parameters on the shape of cold rolled strip.

Various experimental methods have been used to show the effect of different Sendzimir mill rolling parameters on stainless steel strip shape. Experiments using sister coils, noting the effects of change over a number of coils, and using the "Taguchi" statistical experimental design techniques have been carried out. Work has been carried out on individual rolling presses and on complete rolling sequences. Strain measurements have been used to show the behaviour of a statically loaded work roll, and the vertical and horizontal bending of a roll were investigated. From this work the effects of the axially adjustable first intermediate rolls on the strip shape have been further investigated. The parameters that affect strip shape have been identified and stated in order of the magnitude of their effect. The adjustments that are needed to improve specific strip shape defects have been identified. It has been established where rolling parameter alterations have an interacting effect with other rolling parameters. Recommendations have been made that will improve the rolling process to enable a more consistent and better product, over a limited material range, to be rolled. Consideration has been given to new roll shapes and roll bending has been related to specific strip shape. Recommendations have been made to improve the rolling process so as to attain flatter strip