But in analyzing the dynamic characteristics of rolling mill , we find that the system exists nonlinear uncertainty and slow time - variation , which are caused by nonlinear mode and random disturbance . this leads to the approximation of the practical system of the model and parameter and it is difficult to construct the accurate mathematical model . therefore , the routine controlling method is n ' t used any longer 然而,在分析軋機的動態(tài)特性中發(fā)現(xiàn),由于位置內(nèi)環(huán)的模型中存在非線性元件,系統(tǒng)受到過多外界擾動的影響致使系統(tǒng)中存在非線性、不確定因素及慢時變參數(shù)的現(xiàn)象,推導出的模型結構和參數(shù)只是實際系統(tǒng)的一個粗糟近似,難以建立精確的數(shù)學模型,此時,常規(guī)控制方法已不再適用。