Looper Control Research Articles

New tension control at the head of strip in hot strip finishing mill

In this paper, a new tension control scheme is proposed to diminish the width shrinkage at the head of the strip in the hot strip finishing mill. The proposed control scheme is applied before the looper control starts and is composed of three main parts. First, the correlation between the width shrinkage and the current difference of the main motors is analyzed. Second, the tension is calculated from the current difference between the two neighboring stands. Third, the speed of the main motor is controlled by the speed difference between the output of PI controller and the reference speed. It is shown through the field test of the Kwangyang no. 1 hot strip mill of POSCO that the width shrinkage is greatly decreased by the proposed control scheme.

Dynamics and variance control of hot mill loopers

Poor control of hot strip mill loopers degrades strip width and gauge, and may even lead to mill breakdowns due to instability. In this study, dynamics of the looper–strip system and the control challenges it poses are discussed, and covariance control theory is applied to variance control design for loopers. Since looper disturbances have a deterministic nature, and their accurate modelling is a challenge that is not easily addressed, the problem represents a case in which a variance controller has to be designed without an explicit disturbance model. Control performance is assessed on a full-stand, nonlinear high fidelity finishing mill simulator, and comparisons to a conventional control system are provided.

A HOT STRIP MILL TENSION/LOOPER CONTROL USING MPC WITH CONTINUATION/GMRES METHOD FOR PWA SYSTEMS WITH A SEQUENTIAL MODE TRANSION

This paper shows the tension and looper control in the hot strip finishing mill based on PWA (piecewise affine) systems with sequential mode transtion. Therefore, the proposed method in this paper formulate the hybrid model predictive control problem as an optimal control problem with an unknown terminal time, and the terminal condition. The proposed control law is derived by solving nonlinear equations in an on-line manner. It also utilizes the continuation/GMRES (Generalized Minimal Residual) method for solving the nonlinear equations efficiently. Finally, the simulation results are illustrated to show that the proposed method works well.

Development of industrial production of ultrafine grained steel in tandem hot strip mill

Based on a model of microstructure evolution, an appropriate rolling schedule has been worked out to produce ultrafine grained steel (2 to 5 μm) on the hot strip mill. This rolling schedule is characterized by a large reduction in the finishers followed by strong cooling. Implementing such a rolling schedule on a conventional HSM raises major problems: increased rolling torque and force, lowered crown and shape control, disturbed looper control, accelerated roll damage, increased slip between strip and roll, insufficient cooling efficiency. These problems have been solved on the new Nakayama HSM by introducing innovative processes such as: single roll drive with different diameter and a new CVC, curtain wall cooling in the finisher, low inertia hydraulic looper, new high-speed steel rolls with solid lubrication.

A HYBRID SYSTEM APPROACH TO TENSION CONTROL IN HOT ROLLING

Since tension and looper control is the key to successful operations in the hot strip finishing mill, several multivariable controllers have been proposed for it. These controllers, however, can be applied only after the transient response in the start-up phase of each rolling has settled. This paper presents a new control design method for tension control in the start-up phase. A hybrid system approach is taken to describe the discontinuous dynamics of the system and to optimize the tension and looper trajectories simultaneously throughout the start-up phase. Simulation results are shown to compare the control performance with the conventional ad hoc control.

Full Stand Modeling and Tension Control for the Hot Strip Finishing Mill

We describe a looper controller design for a hot strip finishing mill in steel plants. The main function of the looper system is to balance the mass flow of the strip by accumulating material in the middle of the stands. Another function is to control the strip tension which influences the width of the strip. To ensure strip quality, it is very important to control the tension of the hot strip finishing mill. However, because there is a mutual interaction between the looper angle and the strip tension, it is difficult to control the looper system. Previous researches examined only the operation of a single stand. But it is not sufficient to examine the operation and effect of whole stands because the operation is wholly interdependent. In this paper, we present a full model of the hot strip finishing mill in order to more effectively control strip tension. We propose several control methods for the full-stand hot strip finishing mill, denoted as conventional PI, PI with cross gain, and coefficient diagram method (CDM) PID control. In the real plants, there are some problems by using higher order controllers such as LQ, LQG and H∞. By comparison, the PID controller is very simple and easy to apply to all real plants. To that end, we present our findings on PID controls and their potential use in the hot strip finishing mill.

On the full stand modeling and tension control for the hot strip finishing mill with PID structure

We describe a looper controller design for a hot strip finishing mill in steel plants. The main function of the looper system is to balance the mass flow of the strip by accumulating material in the middle of the stands. Another function is to control the strip tension which influences the width of the strip. To ensure strip quality, it is very important to control the tension of the hot strip finishing mill. However, because there is a mutual interaction between the looper angle and the strip tension, it is difficult to control the looper system. Previous researches examined only the operation of a single stand. But it is not sufficient to examine the operation and effect of whole stands because the operation is wholly interdependent. In this paper, we present a full model of the hot strip finishing mill in order to more effectively control strip tension. We propose several control methods for the full-stand hot strip finishing mill, denoted as conventional PI, PI with cross gain, and coefficient diagram method (CDM) PID control. In the real plants, there are some problems by using higher order controllers such as LQ, LQG and H∞. By comparison, the PID controller is very simple and easy to apply to all real plants. To that end, we present our findings on PID controls and their potential use in the hot strip finishing mill.

熱延におけるルーパ制御ゲイン調整の人間モデルとその学習

熱延におけるルーパ制御ゲイン調整の人間モデルとその学習

Adaptive and Robust Control Method with Estimation of Rolling Characteristics for Looper Angle Control at Hot Strip Mill.

In this paper, an adaptive robust control method for looper height control of hot strip finishing mill is proposed. The change in strip tension, which exerts an influence on the width and thickness of the products, is induced by the looper height variation. Accordingly, it is important to control the looper height precisely. The looper control system may suddenly become unstable due to a change in the characteristics of rolled material and an occurrence of the slip between roll and strip while rolling. In order to maintain the control system stable even under these changes, the robust control system has been developed. However, there remained problems of slow response of the robust controller. The reason is that the control gain is set at a low value to assure the stability for the various kinds of disturbances. To solve the problem, it is necessary to set at the appropriate control gain. In this paper, the estimation of a damping coefficient of the looper height control system is carried out to adapt the control gain according to the damping coefficient. The proposed adaptive controller assures both the robustness and a high control performance regardless of the change in rolling conditions and disturbances. Using this method, the looper height control can guarantee both the stability of the looper height control and the high degree of accuracy in control.

열간사상압연기의 루퍼시스템의 ILQ 제어기 설계

열간사상압연기의 루퍼시스템의 ILQ 제어기 설계

Parameter Estimation for the Tension Model in Hot Strip Mills

Since tension and looper control is the key to successful operations in the hot strip finishing mill, several advanced control scheme have been developed by applying model-based approaches. Accurate tension models are essential to design the controllers, but the models include unmeasurable parameters. This paper presents a novel estimation scheme for these parameters. The scheme, based on the recursive least-squares method, utilizes tension deviations caused by roll eccentricity for estimation and requires no other signals for excitation of the system, which makes it very practical. Simulation and experimental results are presented to demonstrate the performance of the scheme.

Hot strip width control method by using looper tension measuring system in finishing mill

A high precision hot strip width control method has been developed in this study by applying an interstand looper tension measuring system at the finishing mill stands. As the width deviation of hot rolled steel strip is closely related to abnormal increase in the interstrip tension, an on-line measuring device of looper tension and a data analyzing system were developed in this study. To determine dominant factors that will cause local width shortage, the logged data sets of bar width, bar thickness, looper tension, and strip thickness along the strip length were correlated with the data set of strip width change. With the result of the correlation analysis, existing sequence control logic and parameters for looper actuator were modified for strip width quality and the gains of the looper control were refined for stable operation during the full passage of rolled strip. The on-line tension measurement and tension feedback control for the looper system, improved the strip travelling stability and reduced strip width deviation in the strip top end region.

Hot strip mill tension–looper control based on decentralization and coordination

Since tension and looper control is the key to successful operations in the hot strip finishing mill, several multivariable controllers have been applied. However, this leads to complicated controllers, which are hard to tune on site. This paper presents a new control method based on decentralization and coordination. First, interactions between tension and the looper are evaluated to ensure the applicability of decentralized control. Then, a decentralized controller based on the two-degree-of-freedom Internal Model Control (IMC) structure is applied. Moreover, impedance control is introduced to retrieve the coordinated action of the looper. The control scheme enables stepwise commissioning of control systems, which is very helpful for on-line tuning.

Fuzzy control algorithm for the prediction of tension variations in hot rolling

It is well known that the production of hot coils in uniform thickness depends on various process parameters such as the material, the number of rolling stages, the reduction ratio of the thickness, the rolling speed, the front and back tensions, the friction between the material and rolls, the rolling temperature, and the rolling force at each stage of rolling. In the present study, the effect of front and back tensions on reducing the thickness deviations of hot rolled steel strips were investigated by developing a fuzzy control algorithm. In order to derive the fuzzy control rules, rigid–viscoplastic finite element simulations were carried out using the material property determined from the production data. A simple empirical relationship obtained under the steady-state condition was used for determining the strip thickness. As a result, the thickness variation was determined depending on the change of the magnitude in the rolling force, which is influenced by the front and back tensions in the rolling of steel strips. The results obtained from the present study can be used to establish a database for looper control in hot rolling processes by determining the effect of the front and back tensions and selected process parameters on the maintenance of the uniformity of the strip thickness. Through this study, the capability and usefulness of fuzzy application in thickness control in hot rolling was clearly demonstrated.

Fuzzy algorithm for calculating roll speed variation based on roll separating force in hot rolling

Thickness control of hot-rolled strips has become an important issue in recent years because of the need for improving the quality of the hot-rolled strip. For this purpose, various thickness control systems such as finishing mill set-up (FSU), automatic gauge control (AGC), and looper control system, have been developed at steel works. Although these systems have greatly improved the quality of the strip thickness, there still exists a small amount of thickness deviation. It is difficult to adequately control by applying conventional thickness control techniques since hot rolling process is a highly nonlinear system in which many process parameters are coupled. In this study, a fuzzy algorithm to calculate the roll speed variations was developed in order to improve the thickness uniformity of hot-rolled strips. Since the strip thickness is mostly affected by the magnitude of roll separating force depending on the roll speed, the strip thickness deviation between the desired and actual thicknesses can be reduced by controlling roll speed. In order to carry out this investigation, slab analysis was carried out to determine the relation between roll separating force and roll speed for various process parameters such as roll speed, reduction ratio, strip entry thickness, and front and back tensions. From the production data, the effective stress-strain rate relations of the materials used in slab analyses were acquired. Based on the analytical results, the relation between roll separating force and roll speed was approximated by a log function. A fuzzy algorithm was developed to determine variations in roll speed according to variations of roll separating force, depending on various ranges of rolling temperature, reduction ratio, front and back tensions, and strip thickness. In addition, simulations to predict roll speed variations for a small amount of thickness deviation were carried out at continuous finishing mills consisting of seven stands and the calculated roll speed variations were found to be reasonable. Thus, the developed fuzzy algorithm might be useful in reducing the thickness deviation in the actual hot rolling mills.

SPRING PARASITISM OF OVERWINTERED EGGS OF LAMBDINA FISCELLARIA FISCELLARIA (LEPIDOPTERA: GEOMETRIDAE) BY TELENOMUS NEAR ALSOPHILAE (HYMENOPTERA: SCELIONIDAE)

New Brunswick experienced its first recorded outbreak of hemlock looper, Lambdina fiscellaria fiscellaria (Guenée) (Lepidoptera: Geometridae), in 1989 (Magasi1990). Since 1993, populations have remained at endemic levels. From 1989 to 1994, when annual egg surveys were conducted (from October to April) on balsam fir, Abies balsamea (Linnaeus) Miller (Pinaceae) to forecast the next years' population for planning foliage protection programs, the egg parasitoids Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae) (Hartling et al. 1991) and Telenomus near alsophilae Viereck (Hymenoptera: Scelionidae) were frequently reared from overwintering looper eggs. We believe two factors can cause an underestimation of egg parasitism rates by Telenomus near alsophilae: (i) eggs parasitized by Telenomus near alsophilae can be difficult to identify, and need to be reared to detect the black shading on the chorion which ranges from a mere dark spot to some gradation of black over the entire surface; and (ii) additional parasitism by this parasitoid might occur in spring. Our estimates of egg parasitism rates were as high as 23% (n = 93) from spring-collected looper eggs incorrectly classified as viable until incubated in the laboratory. We describe part of an experiment that confirms spring parasitism by this species, and illustrate the implications to operational looper control operations.

分散と協調に基づく熱延仕上ミル張力・ルーパ制御

分散と協調に基づく熱延仕上ミル張力・ルーパ制御

Hot Strip Mill Tension-Looper Control Based on Decentralization and Coordination

Since tension and looper control is the key to successful operations in the hot strip finishing mill, several multivariable controllers have been applied. However, they lead to complicated controllers which are hard to be tuned on site. This paper presents a new control method based on decentralization and coordination. First, interactions between tension and the looper are evaluated to ensure the applicability of decentralized control. Then, a decentralized controller based on the two-degree-of-freedom IMC sturucture is applied. Moreover, impedance control is introduced to retrieve the coordinated action of the looper. The control scheme enables stepwise commissioning of control systems, which is very helpful for on-line tuning.

Control of Stink Bugs and Lepidopterans on Georgia Soybeans, 1997

Abstract The efficacy of 5 selected insecticide treatments for control of velvetbean caterpillars, soybean loopers and stink bugs, was evaluated at the Coastal Plain Experiment Station’s Ponder Farm, Tifton, GA. The insecticides were foliar applied on 4 Jun on ‘DP105’ and ‘Boggs’ soybeans that were planted in early Jun. Individual plots were 4 rows wide X 50 ft long with alleys 6 ft wide on each end and 1 border row on each side, arranged in a RCBD. There were 4 replications, 2 per variety. Each spray concentrate was applied with a CO2-powered backpack sprayer with 4 TX-12 nozzles on a 6 ft boom (2 nozzles per row) at 40 psi that delivered 19.5 gal/acre. Each plot was sampled prior to treatment and on 3, 7, 14 and 21 DAT (days after treatment) by taking a 25-sweep sample (15 in diam net) from a single row, and comparing insect densities in the treated plots to those in untreated plots. Soybeans were in the R5 growth stage (pods filling with seeds) at the initiation of the test. On the last sample date, only Boggs was sampled due to the late development (leaves yellowing/falling off) in DP105. All plots were harvested at maturity with a small plot combine. Yields were expressed in bushels per acre adjusted to 13% moisture. The data were subjected to ANOVA and Duncan’s multiple range test (P = 0.05).

Mating Disruption of Diamondback Moth (Lepidoptera: Plutellidae) and Cabbage Looper (Lepidoptera: Noctuidae) in Cabbage Using a Blend of Pheromones Emitted from the Same Dispenser1

Experiments were conducted in commercial plantings of cabbage in spring 1994 and 1995 to evaluate the efficacy of a blend of pheromones for diamondback moth, Plutella xylostella (Linnaeus), and cabbage looper, Trichoplusia ni (Hübner), for disrupting mating when dispensed simultaneously from Yoto-con-S® ‘rope’ dispensers (Shin-Etsu Chemical Co., Ltd., Tokyo, Japan). A 12.1-ha cabbage field was treated with pheromone in 1994 using a blend of (Z)-11-hexadecenal, (Z)-11-hexadecen-l-ol acetate, and (Z)-11-hexadecanol in a 49:50:1 ratio for diamondback moth and (Z)-7-dodecen-l-ol acetate and (Z)-7-dodecen-l-ol in a 98:2 ratio for cabbage looper. The test was repeated in 1995 using a 10.1-ha cabbage field. In 1995, 24.6 ha of cabbage also were treated with a blend of diamondback moth-only pheromone: (Z)-11-hexadecenal and (Z)-11-hexadecen-l-ol acetate in a 50:50 ratio. All pheromone treatments were applied at the rate of 1,000 m rope per ha within 2 wk after the cabbage was planted. Captures of diamondback moth and cabbage looper males in traps baited with synthetic pheromones and mating by laboratory-reared sentinel females in pheromone-treated fields were significantly reduced for 7 to 9 wk post-treatment relative to control areas. Larval infestation data on cabbage were insufficient to establish the effect, if any, of the diamondback moth/cabbage looper combination pheromone treatment on cabbage looper control. In 1995, the diamondback moth pheromone only and the diamondback moth/cabbage looper combination pheromone effectively suppressed diamondback moth larval numbers below the composite economic action threshold of 0.3 larva per cabbage plant for approximately 60 days. A single application of pesticide quickly reduced the diamondback moth larval count below the action threshold in the pheromone-treated cabbage, and no further pesticide applications were required. The correspondent control field was sprayed 7 times with pesticides for control of diamondback moth.