Robust control of the A-axis with friction variation and parameters uncertainty in five-axis CNC machine tools

Abstract

A-axis is an essential assembly in the five-axis CNC machine tools, and its positioning precision directly affects the machining accuracy and surface quality of the parts. Considering the influence of parameters perturbation and uncertain cutting force on the control precision of the A-axis, a nonlinear dynamics model of the A-axis system is established, which reveals the relationships among the drive torque, the load torque, the motion direction and the system parameters. Then, two adaptive sliding mode controllers (ASMC) are designed. The first one is based on the bipolar sigmoid function, which can adjust the switching gain and the boundary layer thickness adaptively, then, equilibrium between the tracking error and the chattering can be achieved. The second one is a compound adaptive controller constituted by the traditional sliding mode controller (TSMC) and an internal controller that is based on the hyperbolic tangent function. When the state trajectory comes into the boundary layer, the TSMC will be replaced by the internal controller, thus, the adaptive controller can continuously switch between these two controllers, which can effectively eliminate the high-frequency chattering in the TSMC. Stability of these two controllers is guaranteed by the Lyapunov theory. Experimental results demonstrate the effectiveness and feasibility of the proposed ASMC, which can smooth the input chattering and reduce the tracking error by 16.62% and 21.44%, respectively.

Real-time implementation of an enhanced nonlinear PID controller based on harmony search for one-stage servomechanism system

“…However, often there is a limitation that increasing order cannot improve the model N.m The DC motor torque accuracy sufficiently. Therefore, it is necessary to explicitly add the nonlinearities into the system [19].…”

Nonlinear dynamic modeling and adaptive sliding control of the milling head for efficient and powerful machining

“…The hydraulic locking mechanism installed on the left side of the shaft can make the motorized spindle locked at any position in the angle range (2120°, 30°), and control system of the milling head is shown in Figure 2. 3,6 Figures 3 (case A) and 4 (case B) show the force exerted on the right side and left side of the worm, respectively. t b is the input torque exerted on the worm, and t l is the load torque imposed on the gear.…”

“…5 Recently, all aspects of the system performance have been improved, but there are few successful cases that take all the indicators into account; thus, it is fairly important to improve the positioning precision and driving torque of the milling head simultaneously. [6][7][8] The milling head used for study is mainly based on the worm gear transmission mechanism; compared with the rolling engagement of the traditional gear transmission, engagement of the worm gear is pure sliding. Therefore, the friction influences significantly on positioning precision of the milling head; usually, friction is considered as a kind of interference for the feedback control of the drive system.…”

Robust model predictive control of a micro machine tool for tracking a periodic force signal

“…Various standard adaptive control methods of machine tools with parametric uncertainties have been developed to guarantee machining stability by making use of online estimation 13 . Robust control of the A‐axis system of five‐axis CNC machine tools subject to parameter perturbation and uncertain cutting forces, which mitigates the input chattering and improves the tracking performance 14 . In addition, sliding mode control to deal with friction and cutting force disturbances is also proposed for control system design of machine tools 15 .…”