Study On Vibration Characteristics And Control Of Rolling Mill Based On Nonlinear Stiffness Of Hydraulic Cylinder

With the progress of science and technology and social development,people pay more and more attention to the vibration problem of the strip rolling mill.Due to the complexity of the mechanical structure of the strip mill and the nonlinear factors in the rolling process,the vibration of the strip mill often occurs.It is urgent to understand the vibration mechanism of the strip mill,and to master the control method of suppressing the vibration of the strip mill.To eliminate the vibration of the strip mill and improve the quality of the rolling product,the vibration characteristics and control methods of the roller system under the constraint of the nonlinear stiffness of the hydraulic cylinder are studied.Firstly,in this paper,aimed at the limitation of the current research on the vibration of the nonlinear strip mill.According to the working mechanism of the hydraulic cylinder and the mechanical mechanism of the strip rolling mill,the expression of the nonlinear stiffness of the hydraulic cylinder is given.The relationship of variation rule between the hydraulic cylinder piston position and the nonlinear stiffness of the hydraulic cylinder is studied.The nonlinear stiffness of the hydraulic cylinder is simplified by Taylor series expansion.This provides a theoretical basis for the study of the roll vibration of the strip mill under the constraint of the nonlinear stiffness of the hydraulic cylinder.Secondly,considering the constraint effect of the nonlinear stiffness of the hydraulic cylinder,the four-roll strip mill is simplified to the spring-mass block by the mass method,and the single-degree-of-freedom vibration model of the strip rolling mill under the constraint of the nonlinear stiffness of the hydraulic cylinder is established.The amplitude-frequency response and bifurcation characteristics of the system under the influence of the parameters such as the nonlinear stiffness coefficient,the external excitation amplitude and the initial displacement of the rodless cavity of the hydraulic cylinder are simulated by the average method.Then,on the basis of the single-degree-of-freedom vibration model of the strip rolling mill,considering the influence of the frame of the strip mill,the frame is equivalentto a mass block,and the two-degree-of-freedom vibration model of the strip under the constraint of the nonlinear stiffness of the hydraulic cylinder is established.According to the D’Alembert principle,the vertical vibration equation of the rolling mill roll with the nonlinear stiffness of the hydraulic cylinder is obtained,and the amplitude and frequency response of the vibration system is solved by the average method.The frequency characteristics,spectral characteristics and time domain characteristics of the vibration system of the strip mill are studied,which provides a theoretical reference for suppressing the vibration of the strip mill.Finally,a kinetic control model of the nonlinear stiffness control system of hydraulic cylinders is established for the single degree of freedom vibration problem of the hydraulic stiffness system.The stability of the hydraulic stiffness system is analyzed by Melnikov method and Lyapunov stability method respectively.The influence of the system parameters on the stability of the nonlinear stiffness of the hydraulic cylinder is obtained.The influence of control parameters on the nonlinear constrained system of the hydraulic cylinder is studied by numerical simulation.The control method of the nonlinear stiffness control system of the hydraulic cylinder is given.It provides a theoretical reference for further study on the dynamic control model of the hydraulic cylinder of the constrained nonlinear systems.