Il Seop Choi

A SURVEY OF THE LOOPER-TENSION CONTROL TECHNOLOGY IN HOT ROLLING MILLS

Abstract Looper and tension control is important in hot strip mills because it affects the strip quality as well as strip threading. Moreover, the most difficult challange in the controller design and control performance comes from the interaction between looper angle and strip tension. Disturbances from several sources also cause a deterioration in control performance, and thus they should be rejected effectively by proper control algorithms. Up to now, various kinds of control schemes have been proposed and applied to this control problem. Recently nevertheless, strict demand for strip quality by the market has required improved approaches to this control area. This paper investigates strong and weak points of various control algorithms proposed in academia as well as industry. It also explores the potential of future technology in this area.

Design and control of multi-degree-of-freedom shroud nozzle hydraulic manipulator in steel manufacturing

This paper presents the design and control of multi-degree-of-freedom (DOF) hydraulic manipulator for the steel-manufacturing work flow automation in continuous casting. This manipulator is aimed at handle a heavy-weight shroud nozzle autonomously in hazardous circumstances around the ladle. The half-sized miniature shroud-nozzle manipulator platform was manufactured, where it is operated by hydraulic-powered actuators. Three rotary and two linear hydraulic actuators compose 5-DOF manipulator and it can generate a stable 800 N tightening force to upright. Each joint link includes a 1-DOF joint torque sensor and encoder, which measure the contact force with the collector nozzle. Since hydraulic actuators can support heavy-weight loads such as shroud nozzles with relatively compact volume, it is suitable for applying in the steel manufacturing processes that allow restricted working spaces. Position-based control method is used for the shroud nozzle to approach the collector nozzle. After contacting two nozzles, the force controller based on a force integral control is applied. Integral equation based controller tends to reduce a force error in process of time. The results of simulation and experiment showed that this manipulator is qualified to satisfy use.

Effectiveness of MPC algorithms for hot rolling mills in the presence of disturbances

The control target in the looper-tension control of HRM (hot rolling mills) is to maintain looper angle and strip tension simultaneously at their desired values. However, the most difficult challenge in the controller design arises from the interaction, between strip tension and looper angle, and uncertainty coming from disturbances and a model mismatch. Recently, there has been some research investigating the potential benefits of MPC (model predictive control) for this control loop. However, most of this used constrained optimization based on nominal models, which often results in constraint violations for the uncertain case. The purpose of this paper is to investigate existing MPC algorithms for disturbances and evaluate their effectiveness for a hot rolling mill process through comparison examples.

A robust MPC design for hot rolling mills: a polyhedral invariant sets approach

The role of a hot rolling mill process is to produce strips of thickness about 0.8 ~ 20 mm from heated slabs. One of the major control problems in hot rolling mills are the looper and tension control loops because these have a significant impact on the dimensional quality of a strip and process stability. Moreover, the most difficult challenge in the controller design arises from the process interaction and uncertainty affecting these loops; uncertainty comes from several sources of disturbances and model mismatch. Recently, some authors have investigated the potential benefits of MPC (model predictive control). However, most authors used constrained optimisation based on nominal models and therefore, recursive feasibility and stability is not guaranteed for the uncertain case. The aim of this paper is to extend previous studies of MPC for rolling mills (Choi, Rossiter and Fleming, 2004) to the robust case as well as to evaluate the efficacy of a recently proposed robust MPC (RMPC) (Pluymers, Rossiter, Suykens and De Moor, 2005) design on a multi-dimensional process

Powered upper-limb control using passivity-based nonlinear disturbance observer for unknown payload carrying applications

This paper proposes a passivity-based nonlinear disturbance observer (DOB) design for a powered upper-limb robot control. The proposed DOB allows for the nonlinearities of the robot dynamics, whereas the typical DOB designs cannot. Moreover, by virtue of the passivity property, human operator and environmental interactions can be embedded in the control loop. As a DOB, the proposed approach has a disturbance observation property that makes the actual robot behave like a nominal model selected by the user. Performance analysis proposes a gain tuning rule. In experimental validation, actual powered upper-limb robot is used to perform unknown payload carrying applications.

An Application of the Model Based Predictive Control in a Hot Rolling Mill

Abstract The conventional PI control scheme has been used widely to control the mass flow and strip tension in a hot strip mill. However, the mutual interaction between the looper angle and strip tension prevents the use of large control gains. Slow and linear actions from the controller may induce severe strip quality defects and instability of the process under abnormal operation conditions. To solve these problems a control scheme based on model based predictive control (MPC) is suggested because of its systematic handing of interactions and constraints. The LQMPC algorithm, which is a relatively conventional MPC design, is implemented for the looper and tension control using the closed loop paradigm (CLP).