冷轧板形调节机构动态交替控制的研究与应用(含中文翻译)-英语论文.doc

冷轧板形调节机构动态交替控制的研究与应用(含中文翻译)-英语论文冷轧板形调节机构动态交替控制的研究与应用(含中文翻译)Research and Application of Dynamic Substitution Control of Actuators in Flatness Control of Cold Rolling MillAbstract: The work roll bending control has a strong ability to eliminate the symmetrical flatness defects of strip. However, if the incoming strip is coming with big symmetrical flatness defects, it happens that the position limit of work roll bending is prone to be reached or exceeded during the execution of the displacement, resulting in the residual symmetrical flatness defects without further elimination, as well as a limited flatness control process. Abilities of work roll bending and intermediate roll bending / sh原文请找 ifting for flatness control have been analyzed, which is based on the actuator efficiencies, for the purpose of solving the problem of work roll bending control reaching threshold. Meanwhile, a self-learning determination model of actuator efficiency factors was developed which can be utilized to determine the actuator efficiency factors online accurately, during normal rolling operation, from the measurement data extracted from the rolling mill. Models of intermediate roll bending and intermediate roll shifting substitution control in case of work roll bending control over-limitation have been developed, in accordance with the practical conditions and the degree of work roll bending over-limitation. Applications show that the substitution control can play an important role in the residual symmetrical flatness control, which should have been eliminated, however, have not been removed completely by the work roll bending control due to its over-limitation.Key words: flatness control; work roll bending; actuator efficiency; substitution control; actuator position limit1 IntroductionThe rising demands from such as auto industry, household electrical appliance industry and so on for the quality of cold rolled strip increasingly demands good strip flatness 1. The UCM cold strip rolling mill is usually equipped with a variety of flatness adjustment actuators, such as tilting roll, roll bending, roll shifting, selective roll cooling and so on. models is crucial to flatness control, to which the establishment of control models of individual flatness actuators is significant 3, 4.Uneven deformation of strip during rolling processes will cause uneven distribution of the tensile stresses across the strip width and unfavorable stress distribution increases the buckles, wave-shape flatness defects, as well as danger of strip breaks 5. Flatness defects can be divided into two forms, i.e., global flatness defects and local flatness defects. The bending roll and shifting roll control are mainly used in the symmetrical flatness defects control of global flatness defects and the tilting roll control is mostly used in the non-symmetrical flatness defects control of global flatness defects 6. Differently from the global flatness defects, the local flatness defects are generally eliminated by selective roll cooling control 7. Generally, the work roll bending control can play well in the symmetrical flatness defects control. However, if the incoming strip has too big symmetrical flatness deviation, the situation comes that the symmetrical flatness defects has not been eliminated completely while the work roll bending control has reached its position limit. For the purpose of avoiding this, some flatness actuators whose position limit has not been reached in flatness control are pre-selected, if anyone of them can be used in the symmetrical flatness defects control, then it will be selected as the substituting actuator for the work roll bending and adjusted within the range of its regulation to eliminate the symmetrical flatness defects that the work roll bending control has not removed completely. It is just the idea of dynamic substitution control of actuators in flatness control, which is studied in this paper. This paper takes a 1250 6-H reversible UCM cold mill as the object of this study, with efficiency factors of individual flatness actuators thoroughly studied, to seek the appropriate actuator for substitution control. Meanwhile, a specific control scheme has been developed for the substitution control to eliminate the symmetrical flatness defects which should have been removed completely by work roll bending control. With the substitution control model, the substituting actuator can be utilized to replace the work roll bending for further symmetrical flatness defects control when the work roll bending has reached or exceeded its position limit, so as to enhance the ability of cold mill for better flatness control.2 Study of actuator efficiency factorsModern high-tech cold strip rolling mill has been usually equipped with a variety of flatness adjustment actuators, such as tilting roll, roll bending, roll shifting and so on8. In practical rolling processes, it requires an integrated use of various means of flatness regulation, aiming at elimination of flatness deviation, by regulating the interaction effect of various flatness adjustment actuators. Therefore, having a correct understanding of the performance of various flatness actuators is the prerequisite to flatness control 9. With the means of engineering calculations and tests progressing, the utilization of the efficiency function to describe performance of mill for flatness control becomes possible 10. Actuator efficiency factors on which the closed loop flatness control system is based on provide the quantitative influence regularity of actuators to flatness control. Assuming the presence of a flatness error, the calculation of the set points for the actuators to be displaced requires accurate knowledge of the actuator efficiency. The strategy of dynamic substitution control of actuators based on the ideas of actuator efficiency factors has been made, in case the work roll bending reaches its position limit. The flatness actuator whose efficiency factors is most similar to the efficiency factors of work roll bending will be determined as the substituting actuator and put into use to eliminate the symmetrical flatness defects that the work roll bending control has not removed completely.2.1 Concept of actuator efficiency factorsIn general, the traditional model of flatness control is based on pattern recognition and decoupling calculation of flatness deviation 11, 12. Fortunately, these complicated processes of pattern recognition and decoupling calculation of flatness deviation can be avoided by the use of actuator efficiency factors. Flatness actuator efficiency which comes from measured stress distribution and corresponding analysis and calculations is no longer limited to linear, quadratic and quartic flatness deviation and so on, and can describe any performance forms of flatness actuators without further pattern recognition and decoupling calculation of flatness deviation 13, 14. Compared with the traditional model, it can realize the comprehensive utilization of measurement flatness information, and is helpful for rolling mill to give full play to the flatness control, as a result of improving the accuracy of flatness control 15. The actuator efficiency for flatness control is the amount of flatness change under unit volume regulation of individual actuator 16, and Eq. (1) gives the expression of the actuator efficiency for flatness control: (1)Where is the matrix of actuator efficiency factor for flatness control, is the adjustment value matrix of flatness actuators, is the matrix of the resulting flatness change value, represents the number of measurement points along strip width and represents the number of actuators for flatness control.2.2 Determination of actuator efficiency factorsThere have been two ways to determine the actuator efficiency factor until now. One is the finite element simulation and the other is from rolling experiments 17. Due to the complex influence of actuators to flatness and mutual influence between them, the efficiency factors are extremely difficult to be determined through the traditional roll elastic deformation theory and the strip three-dimensional plastic deformation theory accurately. In addition, the efficiency factors are and roll shape. Therefore the actuator efficiency is difficult to determine by rolling experiments or offline models accurately.In the study of dynamic substitution control in case of work roll bending reaching limit, a self-learning determination model of actuator efficiency factors was developed which can be utilized to 1431冷轧板形调节机构动态交替控制的研究与应用(含中文翻译)determine the actuator efficiency factors online, during normal rolling operation, from the measurement data extracted from the rolling mill. The self-learning determination of the efficiency factors assumes apriority knowledge with default set parameters and subsequently improving this knowledge with the aid of prescribed learning processes. These processes are not dependent upon individual activation of the various actuators. The flatness control activates one or several actuators simultaneously in normal rolling mode, dependent upon the measured flatness. Subsequently the displacement variable change as well as the resulting effects on the strip tension distribution are measured and evaluated for the determination of the actuator efficiency. To determine the apriority efficiencies, the operating point parameters which correspond to a pair of rolling force and strip width parameter were recorded. The actuators were at the beginning of commissioning displaced individually by hand and the resulting flatness change was determined. From the relation between actuator displacement and flatness change, the associated efficiencies were calculated, which then served as apriority efficiencies, on which the self-learning processes is based. This procedure was carried out for several strip widths. Based upon this knowledge, actuator efficiencies could already be calculated, which, however, did not exactly correspond to the response of the rolling mill in question. Self-learning processes were implemented to improve the match to the response. They recorded actuator changes strip after strip, together with the resulting changes in flatness parameters. In this way also changes of actuator efficiencies caused by mechanical changes could be detected. This ensured that the match of the calculated actuator efficiencies to the actual eff原文请找 ects in the rolling mill was continuously improving.Fig. 1 gives the actuator efficiency factor curves determined by the self-learning determination model of the 1250mm cold mill of an operating point corresponding to the roll force 7520kN and the strip width 990mm.Fig. 1 Curves of efficiencies of actuatorsIn Fig. 1, all of the efficiency factor curves for work roll bending, intermediate roll shifting and intermediate roll bending show that their influence on strip flatness are symmetrical, which can be utilized to eliminate the quadratic and more complex symmetrical flatness defects. The efficiency factor curves of tilting is non-symmetrical that can be utilized to eliminate the linear flatness error. In addition, the fluctuations of roll force interfere with flatness control severely.2.3 Determination of substituting actuators through actuator efficiency factorsAnalyses of actuator efficiency factors determined by self-learning processes have been made to find out the suitable substituting actuators which should have a similar effect to flatness as the work roll bending. The 1250 single stand 6-H reversible UCM cold mill has been equipped with four actuators which are the work roll bending, the intermediate roll bending, the intermediate roll shifting and tilting roll, respectively. The actuator efficiency factors of them are shown in Fig. 1.As shown in Fig. 1, the efficiency factor curve of work roll bending looks like a parabola and has big slope coefficient in whole, which means the work roll bending is powerful in symmetrical flatness defect control. However, the slenderness ratio of work roll is so large that it may occur with roll edge deflection when imposed with bending forces, especially for wide strip rolling mill, leading to weak central strip flatness control. This also can be explained by the shape of the efficiency factor curve of work roll bending shown in Fig. 1. As shown in Fig. 1, the efficiency factor curve of work roll bending is not entirely a parabola shape distribution but with two inflection points in the region of central strip. The efficiency factor curve tends to be a horizontal line between two inflection points with corresponding slope coefficient decreasing almost to zero. This indicates that the work roll bending has no power in the flatness control of central strip. If huge flatness defects appear in central strip, the work roll bending is easy to reach or exceeded its position limit when try to eliminate the flatness deviation thoroughly. Moreover, blindly increasing of the work roll negative bending force will result in the edge touch and deformation of work rolls beyond the edges of the strip, in return leading to accelerated roll wear 18.The efficiency factor curves of intermediate roll bending and shifting also look like parabolas, but with small slope coefficients. Thus it seems that they have less power in flatness control than the work roll bending control. In fact, both of them can be utilized to some extent to eliminate the symmetrical flatness defects. In addition, deflection and deformation near the roll necks can be avoided because of the larger diameter of intermediate rolls, as well as the flatness in control without edges of strip interfered.Based on theaid of the optimal control algorithm, the flatness control system firstly calculates the adjustment displacements of tilting roll, work roll bending, intermediate roll bending and intermediate roll shifting based on the actuator efficiency factors and the corresponding measured flatness deviation. If the actual displacement path of work roll bending has reached or exceeded its position limit, the check of finding out whether the actual displacement path of substituting actuators such as the intermediate roll bending / shifting also has or has not reached or exceeded their position limit will be implemented. If anyone of them has not reached or exceeded its position limit yet, the control mode of dynamic substitution control will be switched on. Otherwise, normal control mode will be turned on. The dynamic substitution control of actuators can be illuminated by Fig. 2.Fig.2 Block diagram of the dynamic substitution control of actuatorsAs shown in Fig. 2, Lim_ib and Lim_is are respectively the position limits of intermediate roll bending and intermediate roll shifting. Lim_wb represents the position limit of work roll bending.3.1 Closed-loop feedback flatness controlThe calculation model of closed-loop feedback flatness control used is based on actuator efficiency factors, using liner least squares principle to establish an evaluation function, by which the optimal actuators adjustment can be determined according to actuator efficiencies and flatness deviation. The evaluation function can be expressed by Eq. (2): (2)Where is evaluation function, is weighting factors of the deviation between set point and actual value at the location number , is specific strip tension deviation for each measurement zone, is the additional displacement path to be calculated of the number actuator, is 冷轧板形调节机构动态交替控制的研究与应用(含中文翻译)number of measurement zones and is number of actuators, and are the measurement zone number and the actuator number, respectively. The weighting factors permit the deviation between set point and actual value over strip width to be factored differently. Therefore the deviation at the strip edges can be factored higher than the deviations in the strip centre area. Minimization of the function will permit determination of unknown additional displacement path , i.e., additional displacement paths of the tilting roll uT, the work roll bending uWB, the intermediate roll bending uIB and the intermediate roll shifting uIS, which can be shown as Eq. (3): (3)Dependent on actuator efficiency factors and flatness deviation, the closed-loop feedback flatness control system calculates individual actuators displacements one by one. In order to guarantee that the relationship of the calculated displacement values remain constant, as far as necessary, it is essential to check whether the position limits of individual actuators are exceeded or reached during the execution of the displacement. It is necessary to ensure constant displacement relationships between actuators with similar effect and differing displacement speeds.3.2 Substitution control models of work roll bendingTwo forms of substitution 原文请找 3.2.1 Mode A of substitution controlIn mode A, it assumes that the displacement path limit of work roll bending has been reached or exceeded in roll process, which can be expressed by Eq. (4): (4)Where represents the actual value of work roll bending, represents the positive position limit of work roll bending, represents the constraint factor of position limit of work roll positive bending.It may also be the case that the negative position limit of work roll bending has been reached or exceeded, which can be expressed by Eq. (5): (5)Where represents the negative position limit of work roll bending, represents the constraint factor of position limit of work roll negative bending.To avoid activating / inactivating treatments on small variations of a signal near a threshold value, a hysteresis term “