Study On Stability And Control Of Strip Rolling Mill’s Main Drive Torsional System Under Time Varying Parametric Excitation

With the requirements of the gradually increased rolling speed and rolling strength, the rolling mill requires a more stable, more accurate and higher dynamic performance, it is true indeed that increasing the rolling speed can improve production efficiency, but unavoidably excessive rolling speed can easily lead that the drive system frequently occurs the abnormal dynamic instable phenomenon of torsional vibration, frequent vibration cumulative even cause damage to equipment and structural components of mill, seriously affect the normal operation of the production line, which will cause huge economic losses to the country, business and people.In this paper, the strip rolling mill’s main drive system is studied. The time-varying parametric excitation nonlinear torsional vibration behavior of the rolling mill’s drive system is induced deeply, the instability mechanics of the torsional vibration of the drive system under the effect of external load driving force, shaft angle and nonlinear clearance and other nonlinear aspects are revealed in the nature of nonlinearity. Through amplitude-frequency characteristic, bifurcation characteristic, chaotic characteristic analysis of the system, theoretical guidance for time-varying parametric excitation stability of the strip rolling mill’s main drive system are provided.Firstly, considering the nonlinear factors of the rolling mill such as external load driving force, shaft angle and nonlinear clearance and other nonlinear aspects, mechanical models of the two-degree-of-freedom of time-varying parametric excitation torsional vibration of the strip rolling mill’s main drive system were established based on the principle of generalized Lagrange, which provides a theoretical basis for the precise analysis of torsional vibration characteristics of the strip rolling mill’s drive system.Secondly, according to the established time-varying parametric excitation torsional vibration mechanics model of the rolling mill, the dynamic response of the rolling mill’s torsional vibration dynamics equation has been deduced by using nonlinear vibration theory multi-scale method under the combined effects of parametric excitation and external excitation, the system’s amplitude-frequency characteristics are studied under primary resonance- basic parameters and 1/2 subharmonic resonance. And by using singularity theory the stability of the system is investigated, the bifurcation topology have been given in different unfolding area.Thirdly, the heteroclinic orbits of the time-varying parametric excitation torsional vibration mechanics equations are obtained by using Melnikov method and the system’s conditions of chaotic threshold are given. Numerical simulations of global bifurcation and chaotic characteristic are studied, using phase trajectories, Poincare section and the largest Lyapunov exponent verify the validity of the theoretical analysis.Finally, on the basis of above theory, the time-delay position feedback control has been introduced into the two degree of freedom’s relative angle of the time-varying parametric excitation torsional vibration system, and the system’s resonance regions and system’s stability are studied under time-delay position feedback control. According to control feedback parameters, observe safe basins’ fractal morphology, the stable values of the system’s feedback parameters are given.