Abstract: In order to solve the automatic control problem of [?]8.8 m×4.8 m semi-autogenous mill in a domestic mine， the system control design research was carried out using the expert PID control system. The results showed that: ① There are many factors affecting the condition of semi-autogenous mill， mainly including ore properties， grinding media， feeding rate， grinding concentration， state of liner and grid plate and so on. Material filling state can be judged from power of semi-autogenous， axial pressure and grinding sound， and the material level control can be realized by adjusting the amount of feeding， water supply and ball addition. ② Compared with traditional PID algorithm， expert PID algorithm has distinct advantages. Expert PID essentially adopts nonlinear design method and introduces expert experience into the formulation of control strategy， which is more suitable for the implementation of complex object control strategy. Thus， it overcomes shortcomings of conventional PID better， such as poor adaptability to nonlinear system， and difficult to overcome abnormal disturbances and determine the lag time constant. ③ On the basis of fully considering the working characteristics of the semi-autogenous mill， the designed expert PID control system can stabilize the axial pressure and power of the semi-autogenous mill within the set value range. At the same time， it can judge whether the semi-autogenous mill is in the stable state， according to the comprehensive analysis of parameters， such as feeding， water supply， hard stone volume， and grinding sound of semi-autogenous mill.

Key words: Semi self mill, Expert PID, Control system