Research On Adaptive Variable Structure Control For Gauge Control System Of Cold-Strip Rolling Mill

Hydraulic servo automatic gauge control (AGC) system of cold rolling mill is a class of complicated system with nonlinearity, time-varying and parameter uncertainties. Traditionally, PID control was widely employed in the AGC system for its maturity in technology, easy-mastered for technician, and so forth. However, model parameters change in different degree in practice, as a result of disturbances of load, oil temperature, the degree of hardness undulation, as well as the differences in the work pieces and equipments condition. In addition, there exist internal and external parameter uncertainties. Recently, modern control theory develops rapidly, providing a possibility to design controller which is liable to attenuate parameter uncertainties and external disturbances, so that the quality of production can be improved. So far, some of these advanced control theories have already been adopted in practices.First, a mathematical model is established in form of space-state equation for the hydraulic servo position system. Then the model of AGC control system is erected based on the time-delay process of gauge detect device, and the parameters are given accordingly.Secondly, a controller design method which uses adaptive variable structure control theory is claimed for the AGC system of cold rolling mill with input dead zone, parameter uncertainties and external disturbances. In order to depart the section with control input from the original system, a linear transform is adopted. Then by construction of Lyapunov function and solution of LMI (linear matrix inequation), the sliding mode surface of this time-delay system is obtained. Secondly, in view of the nonlinear dead-zone, an adaptive method is adapted to estimate the slope of the dead-zone. Meanwhile the system uncertainty parameters'boundary is estimated so that the uncertainty will not be necessary to satisfy the uncertainty match condition and the asymptotical stability of the system is guaranteed.In addition, considering the input saturation of controller in hydraulic servo position system with parameter uncertainties and external disturbances, an adaptive variable structure controller is designed, which includes the estimate of the lower limit of saturation function. The asymptotical stability of this system is proved by construction of an appropriate Lyapunov function.Finally, the variable structure control problem is studied for discrete-time system which is mentioned in chapter two. An improved discrete reaching law is presented for the controller design of this kind of system. The parameters are selected based on reaching condition. The control law was properly improved considering the state and input time-delay. Meanwhile it also solves the problem of the system chattering and the large scale of the controller's output. It is illustrated by both of the theory analysis and simulation results that the designed controller with the improved reaching law can not only ensure global asymptotic stability of the system, but also confine the output of the controller into certain accredited boundary.