Study On Dynamics And Stability Control Strategy Of The Nonlinear Vertical Vibration System Of Rolling Mill

Facing the increasingly severe constraint of resource and environment, and the contradiction between capacity and demand, as the primary production process, strip rolling production needs further transformating and upgrading. However, vibration phenomena occurs frequently during high speed rolling of strip mill, which hinders the development process of rolling production toward high efficiency, and performanced focus on the vertical vibration produced between frame and rolls system, which is the main reason that damaging the stability of rolls system and cause fluctuation of rolling thickness. Therefore, in order to improve the stability and precision of rolling mill, and improve the quality and performance of rolling products, the vibration behavior influenced by various nonlinear factors and the corresponding restraint strategy of the strip rolls system are researched in this paper.Firstly, the influence of nonlinear factors on vibration behavior are studied, which contains the hydraulic cylinder nonlinear arising from the different elastic modulus between piston rod and hydraulic oil, the nonlinear friction between the hydraulic cylinder piston and cylinder wall, the dynamic characteristics of rolling force and the deformation hysteresis characteristics of rolled piece.Secondly, the strip rolling mill system is simplified as a spring-mass model by the concentrated mass method. According to the generalized dissipative Lagrange principle, the vibration models of strip rolls system are established respectively under piecewise nonlinear constraints of hydraulic cylinder, the influence of the dynamic characteristics of rolling force as well as nonlinear hysteresis deformation of rolled piece. On this basis, a dynamic model with double piecewise nonlinear constraint about elasticity and damping is established. The periodic response characteristics of rolls system are analyzed respectively by considering the influence of nonlinear stiffness and friction of the hydraulic cylinder, rolling speed and external excitation, and then the influence law of each nonlinear factor on amplitude frequency characteristic and stability of rolls system are obtained.Then, the dynamic response of each nonlinear vibration model is obtained by average method and incremental harmonic balance method, transition sets are solved though singularity theory in three different constraints, bifurcation topology of vibration system of strip rolling mills is obtained by choosing unfold parameters in each subdomain divided by transition sets. Based on the bifurcation diagrams and the maximum Lyapunov exponent curve of the system, the bifurcation behavior of the rolling system changing with the rolling speed, the excitation amplitude and frequency is analyzed respectively. The critical values of these parameters are obtained when the system is unstability because bifurcation. Melnikov method is used to obtain the conditions for the occurrence of chaos in piecewise nonlinear systems, and then the corresponding time delay state feedback control strategy is proposed.In the end, the experiment research is carried out in the rolling production line by building the vibration test platform of the rolls system. The validity of nonlinear vibration model of the roll system and analysis results are verified by comparing the simulation results with the experimental results.The research will make up for the deficiency of theoretical research on vibration modeling and dynamic characteristics of strip rolling mill system. In view of the piecewise nonlinear constraints in hydraulic system of the strip rolling mill, the vibration control strategy is proposed. The research results have important significance for improving the rolling speed and rolling accuracy, which is important for improving the stability and the quality of the product.