Research On Friction Modeling And Compensation Of CNC System

The development of high-performance numerical control systems is one of the major special projects of my country’s medium and long-term scientific and technological development plan,and is of vital significance to the processing of key parts and components in the defense and military industry.With the support of relevant policies,researchers have achieved a series of breakthrough research results in the field of CNC systems,gradually narrowing the gap with developed countries.However,the nonlinear friction ubiquitous in the CNC system will cause low-speed crawling,tracking dead zone and other phenomena,which seriously restricts the system’s response quality and tracking accuracy.In order to solve this problem,the paper is based on an open numerical control experiment platform to conduct friction modeling and compensation research to reduce the impact of friction on system performance.The research contents are mainly divided into two parts: model-based friction compensation and adaptive friction compensation.A friction compensation strategy based on Lu Gre model is proposed.An improved quantum genetic algorithm(IQGA)is designed for Lu Gre model parameter identification.The algorithm adjusts the size of the quantum revolving gate adaptively according to the evolution process of the population as a whole,and improves the overall performance of the algorithm.The static parameter identification is based on the steady-state speed-torque curve.The dynamic parameter identification simulates the pre-slip phase of friction through a low-frequency and low-amplitude current excitation signal.The collected data is optimized through IQGA to obtain the identification value of the dynamic and static parameters.In order to improve the robustness of the system,the Lu Gre feedforward compensation and fuzzy adaptive PID are combined,and the simulation of compensation to friction model with changing parameters verifies that the strategy can maintain high tracking accuracy under parameter perturbation.An adaptive sliding mode friction compensation strategy is proposed.The design of the control law is based on Lyapunov’s second method,which ensures the asymptotic stability of the system,and at the same time realizes the estimation of some physical parameters and friction parameters.Aiming at the unmeasurable state quantity in the control law,a sliding mode observer is designed,and the quasi-sliding mode theory is applied to weaken the chattering phenomenon of sliding mode control.The composite disturbance simulation experiment verifies the effectiveness of the adaptive sliding mode control strategy.Based on the Twincat C++ platform,the friction parameter identification and servo experiments of compensation method based on friction model are carried out.Experimental results show that the lowspeed servo performance of the system is significantly improved after the friction compensation module is integrated.