Yaoyao Shi

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

Milling head is an essential assembly in the five-axis computer numerical control machine tools, positioning precision of which directly affects the machining accuracy and surface quality of the processed parts. Considering the influence of nonlinear friction in the transmission mechanism and the uncertain cutting force disturbance on the control precision of the milling head, the static and dynamic performances of the milling head are analyzed; relationships among the drive torque, load torque, motion direction and system parameters are discussed; and, finally, nonlinear dynamic model of the milling head is established. A novel adaptive sliding mode control scheme based on the variable switching gain and the adjustable boundary thickness is proposed for this nonlinear dynamic model; the stability of the closed-loop system is guaranteed by the Lyapunov theory. Experimental results show that the proposed adaptive sliding mode control can reduce the chattering in the traditional sliding mode control and can achieve high control precision without knowing the boundaries of uncertainties in advance.

Precision tension control technology of composite fiber tape winding molding

During the composite fiber tape winding process, tension fluctuation has a serious impact on the performance parameters of winding products, such as strength, compactness, resin content, fatigue resistance, and stress uniformity. Because of the influence of dynamic performance of tension control system caused by the torque motor, external disturbance, sensitivity of the parameter variation, inverter dead zone, ripple torque, cogging torque, nonlinear friction, and measurement noise, a fuzzy proportion integral derivative (PID) controller based on robust extended Kalman filter (REKF) is proposed, which considers membership function optimization of nonlinear dynamic fuzzy control system as systematic identification through designating activated membership function of input and output variable in each control step, and then, online adjustment of the activated membership functions is used to reduce the control error by REKF. By adjusting the shape and position of membership function, the designed controller can be adapted to the dynamic conditions. Simulation and experimental results show that overall performance of the control system has been significantly improved. Compared with traditional fuzzy PID, the fuzzy PID controller based on REKF has strong anti-interference performance and robustness, and the winding tension control precision has been increased by 40–42%.

A formulation of tooth deformation and its error compensation for worm gear transmission mechanisms

Milling head and rotary table are the key components in five-axis CNC machine tools. However, tracking and positioning precision of these rotary axes based on worm gear mechanisms are affected by the backlash, friction, elastic deformation, and other nonlinearities. Therefore, finding out a simple and universal principle to predict the tooth deformation in an initial design is quite significant. A novel deformation calculation and compensation method with finite element analysis and circular plate theory is proposed for the worm gear transmissions. When the relationship (form factor) between the solutions of circular plate theory and finite element analysis is derived, deformation calculation with finite element analysis can be replaced by multiplying the solution of circular plate theory and the form factor. Analysis and calculation results show that the presented method can provide a reference for the compensation control of the positioning errors.