Study On Stability And Control Of Mill Roll System Based On Nonlinear Constraint Of Rolling Force And Friction Force

With the development of society,the size precision and surface quality of strip steel have been put forward higher requirements.However,the vibration of strip mill is easy to cause the thickness error and the surface vibration of strip steel,which greatly limits the high-speed production of strip steel.In order to improve the stability and efficiency of the rolling mill,the stability and control of the rolling mill constrained by the rolling force and friction force are studied in this paper.First of all,considering the influence of horizontal vibration of rolled piece,rolling speed will be improved as the form of roll rotation speed plus the horizontal vibration speed of rolled piece.Based on Hill rolling force formula and Roberts friction coefficient formula,the model of dynamic rolling force and dynamic friction force that is affected by horizontal vibration of rolled piece is established.The rolling force data were collected on the spot,and the validity of the model was verified by comparing the numerical error of rolling force before and after optimization.Secondly,considering the symmetry of the mechanical structure and the vibration characteristics of the rolling mill,the vibration model of the roll system is established by using the lumped mass method.According to the principle of Lagrange generalized dissipation,the coupling vibration dynamic balance equation is constructed respectively along the rolling line direction and perpendicular to the direction of rolling roller rolling line.Again,the amplitude frequency response equation considering the system main resonance and internal resonance is obtained by using the method of multiple scales,which lays the foundation for the amplitude frequency characteristic analysis of the rolling mill.According to the singularity theory,the bifurcation equation of the system is obtained.And in 6 cases,the transition sets and bifurcation topology of the roll vibration of rolling mill are presented.Then,the bifurcation diagram of the rolling mill vibration amplitude with the rolling force is studied,and the critical value of the bifurcation instability is obtained.At the same time,to strip the horizontal vibration velocity is zero as the standard,the roll gap frictionstate is divided into two kinds of static friction and sliding friction.On this basis,the amplitude frequency response under two kinds of friction conditions is simulated and compared.The results show that the sensitivity of sliding friction under the condition of rolling mill vibration of external excitation and internal nonlinear parameters is much higher than the static friction conditions,and it proves the necessity of considering the horizontal vibration of rolled piece.Finally,the rolling mill control function with vibration displacement and velocity feedback is designed,and applied to the dynamic equilibrium equation of rolling roll.By using the method of multiple scales,the system resonance and internal resonance amplitude frequency response equation considering the controlled system are obtained.By adjusting the feedback gain coefficient and time delay parameters,the stability of the vibration limit cycle amplitude and amplitude frequency characteristics of the roller system is controlled.In addition,the bifurcation behavior of the roll system in the main resonance condition is controlled,and the stability of the rolling system is improved.