Study On Unstable Oscillation And Controll Method In Rolling Mill's Torsional Vibration System

The main drive system is one of the most important parts in rolling mills, and the torsional vibration is more outstanding with the rolling speed improving. The steel products'quality and yield are obviously influenced when the torsional vibration occurred in rolling mills, further more, the rolling equipments can also be destroyed, so the research about the torsional vibration is very significant for modern steel industries.The main drive system of rolling mill is consists of some elastic units, and the spindles can be induced vibration while the energy of rolling is transferred. The linear model, nonlinear model and coupled nonlinear systems are studied for their model, stability and control in this paper. The rule of unstable vibration and control method are analytically given, and theory of rolling mill's vibration and its application in engineering are improved.Nonlinear stiffness, structure damping and friction damping are considered, and the dynamics equations are established according to Lagrange theory. The magnetic energy of air gas in AC motor is included, and high dimensional coupled dynamics equations can be established on the basic of Lagrange-Maxwell principle. Above all these works can provide effective models for the dynamics performance analysis and control methods.The stability of linear torsional vibration system in rolling mill is analysed according to Lyapunov theory, and it is studied that causes the main spindle vibrate. Robust and robust stability are also studied based on H∞theory, and an improved H∞control method is proposed through the research for H∞mixed sensitivity function and the robust performance.Using the Hopf theory, the bifurcation is studied for obtained nonlinear torsional vibration systems of rolling mill, and it is given that necessary and sufficient condition of Hopf and the type of unstable vibration. Using multiple time scales and harmonic balance method, the dimension of electromechanical coupling system can be deduced, and double Hopf bifurcation and stability of periodic motion are studied while the system is disturbed by electronic parameters, at the same time the condition of unstable vibration and vibration character can be revealed.To avoid subcritical bifurcation, the bifurcation control method is studied in some torsional vibration system who has nonlinear damping, coupled nonlinear stiffness or electromechanical coupled parameters, and a nonlinear feedback controller is proposed in order to transfer the bifurcation point and make the periodic motion stable, and the amplitude of periodic motion can also be controlled by obtained normal form; A delay nonlinear control method is studied in some typical systems which include nonlinear stiffness, coupled nonlinear stiffness or coupled nonlinear damping. It is studied how the delay time in linear feedback parameter influence Hopf bifurcation point by frequency-domain analysis, and the stability of periodic motion can be controlled through the research for the relation between stability and nonlinear delay time and these research can provide an effective method against unstable vibration in engineering.A measure and control system is constructed about the rotary machine, and some conclusions are validated under the condition of nonlinear factors considered with the aid of torsional vibration platform, and control method can also be validated through the frequency control.