Dynamic modeling and adaptive sliding mode control of A-axis for efficient and powerful milling

Positioning precision of the A-axis as an essential assembly in a 5-axis CNC machine tool directly affects the machining accuracy and surface quality of the machined parts. Considering the influence of parameter perturbation and uncertain cutting force on the control precision of the A-axis, this paper analyzes the static and dynamic performance of the A-axis, discusses the relationships among the drive torque, load torque, motion direction and system parameters, and finally establishes a nonlinear dynamic model of the system. On the basis of this model, an adaptive fuzzy sliding mode control (AFSMC) is proposed. The fuzzy system is used to approximate the nonlinear functions in the sliding mode control law, and adaptive laws of the tunable parameters are designed based on Lyapunov theory. Meanwhile, the exponential reaching law is utilized in switching mode control (SMC). Experimental results show that the proposed AFSMC is robust to parameter perturbation and uncertain load torque. Compared with the traditional sliding mode control (TSMC), the proposed method can effectively reduce control input chattering and improve the tracking precision by 14.54%.