Study On Roll Eccentricity Control For Flat Rolling Mill

Accuracy of thickness is one of main index of plate and strip quality, and roll eccentricity is major factor which causing periodic thickness deviation. Amed at roll eccentricity on flat rolling mill, how to effectively restrain and compensate roll eccentricity in AGC is studied in this paper. The existing problems of roll eccentricity control are mainly as follows:A. Accuracy and strong flexibility of roll eccentricity arithmetic; B. Phase lag and amplitude decay occur when roll gap system compensates roll eccentricity; C. Hardware and software of the realization of roll eccentricity control. According to these problems, some roll eccentricity arithmetic and control schemes are presented, then experiments are made, and the result of experiments is good. The main study in this paper are as follows:1) Study of roll eccentricity control model. Base on the analysis and class of roll eccentricity reason, one, tow and four roll eccentricity caused by rotary eccentricity, roller ellipse or both is analyzed in turn. Roll eccentricity law of all kinds of case consists of following:(1)Period of roll eccentricity signal; (2)Relationship between original phase of each component of roll eccentricity and the maximal or minimal fluctuation range of total eccentricity; How to confirm the parameters of main component and simplify roll eccentricity model; Then the beat of roll eccentricity caused by the difference between upper and lower backup roll diameter is studied; Roll eccentricity characteristic is summarized and the uniform roll eccentricity model is established; Then one new optimal phase control scheme is presented to decrease and conquer the disadvantage of roll eccentricity.2) Study of Fourier transform of roll eccentricity signal. Base on the study of difference and relationship of four kinds of Fourier transform, FFT, spectrum leakage and picket fence effect, a new modified FFT algorithm sampled by Harming window(HMFFT) is presented, and the modified frequency formula, amplitude formula, phase formula of HMFFT are deduced in detail. The characteristic of HMFFT is as follows:(1) High degree of accuracy, especially the accuracy of phase. It can effectively reduce the estimate error caused by the spectrum leakage and picket fence effect of FFT when no complete alternation sample; (2) Calculation is simple and fast. It uses the result of FFT and then is calculated in frequency-domain. Only twice complex calculation is added compared with FFT; (3) Application range is wide. It can be not only used for the thickness deviation diagnosis of strip but also roll eccentricity compensation. 3) Study of threshold method of wavelet transform for roll eccentricity control. For there are some disadvantages in the conventional FFT and other identification arithmetic of roll eccentricity control, a new threshold method of wavelet transform for roll eccentricity control is presented, which uses the property of multi-resolution. A new AGC scheme based on this atuo optimizing threshold method of wavelet transform(AW-AGC) is presented. The characteristic of AW-AGC is as follows:(1) It can accuately identify the roll eccentricity signal when roll eccentricity frequency is variable in sample time and there is difference between upper and lower backup roll diameter, and the roll eccentricity model calculated by this arithmetic is the optimal estimation of real roll eccentricity; (2) It can not only reduce the direct disadvantage of gauge deviation caused by roll eccentricity, but also avoid the labefaction of control effect of GM-AGC; (3) This system has the property of good adaption, strong robustness, high control accuracy.4) Study of phase lag and amplitude decay when general AGC compensating roll eccentricity. The relationship between frequency-domain characteristic of roll gap control system and phase lag and amplitude decay when roll eccentricity compensated, and the infection of compensation result caused by phase lag and amplitude decay are studied; A novel multiple control scheme is presented, which based on the PI control and inserted repetitive control, and the structure of the new system and the method of important parameters tuning are described in detail; The structure of the proposed control scheme is simple; New control scheme can be easily designed and realized; Dynamic and steady characteristic of the system designed with new control scheme are quite fair; The novel system can realize the efficient and highly accuracy compensation of AGC and roll eccentricity.5) Design and application of roll eccentricity control system. Base on a cold mill of laboratory, hardware and software system for roll eccentricity control are designed and level 1 and level 2 with regard to roll eccentricity control is programmed. Then experiments are made used HMFFT and A-WAVELET individually. The rolling force fluctuation range of experiments results is reduced 53.6% or 61.8% individually.