Study And Application Of Strategy To Improve Gauge Accuracy For Tandem Cold Mill

With the development of modern industry, the demand for strip thickness accuracy of tandem cold mill is becoming critical. The control strategy about improving thickness accuracy is the key research of rolling automation. So the study was carried out on thickness preset mathematical models, automatic gauge control, roll eccentricity compensation and so on. Based on the research findings, an automatic control system about thickness was developed and applied in 5-stand tandem cold mill of a certain cold mill plant, which had good performance. The main work is as follows:1) Load distribution methods for tandem cold mill were analyzed. A new multi-object optimization method based on cost function was adopted. By evaluating the characteristics of tandem cold rolling techonology, the appropriate mathematical models and its self-adaptive factors'structure for on-line rolling process control were developed and validated with actual data.2) Taking the mill's sensor configuration into account, a set of comprehensive automatic gauge control system was designed and developed. By improving control algorithm and structure, multiple AGC independency and thickness-tension synchronous decoupling were implemented. In order to eliminate the effect caused by entry thickness deviation, a special feed forward AGC control strategy with the consideration of actuator dynamic model was developed. According to the actuators of stand 1 and stand 5 monitor AGC, Smith predictors with two kinds of models were developed.3) A set of roll eccentricity compensation system based on fast Fourier transformation method was developed. The phase compensation during roll eccentricity signal acquisition and restitution was solved. In accordance with eccentricity source signals'variety during continuous cold rolling process, The results of REC control were analyzed and compared with different source signals. By evaluating the results, a conclusion that the best eccentricity source signal for TCM is inter-stand tension was drawed. FFT-REC is an universal roll eccentricity compensation algorithm for full roll stack and higher harmonics of tandem rolling mill.4) Monitor AGC via gap of stand 1 was mainly investigated. The transfer function of MON-AGC system was deduced. In accordance with features of dead time in MON-AGC, a new intelligent optimum Smith predictor was developed. In order to solve strip thickness oscillation problem with traditional MON-AGC, Smith predictor was introduced. The predictor model was reduced from complicated transfer function by the optimal reduction algorithm. So it has higher accuracy and can be implemented easily. For the purpose of improving robustness and decreasing the sensitivity due to rolling condition changing, a set of intelligent optimum Smith predictor for MON-AGC was developed.5) The thickness control results were analyzed in time domain and frequency domain. A convincible evaluation for control strategy was made.The results of the study are practical for thickness control of tandem cold mill. The improved optimum control strategy has been applied in 5-stand tandem cold mill of a certain cold mill plant. It is benefit to the computer control level of tandem cold mill in China.