Research And Application On Sliding Mode Contouring Control Method Of Biaxial Motion Control System

With the increasing requirement for the high precision of the industrial applications,the contour accuracy of the multi-axis motion control system also has a high requirement.Biaxial motion control system is a very representative multi-axis machining platform,which has been widely used in the contouring machining and manufacturing.In practical applications,the accuracy of contour processing is often affected by nonlinearities such as friction and backlash,as well as external disturbances,which reduce the performance of the system.Therefore,it has a great application background and significance to design suitable contour control algorithms,which can reduce or eliminate adverse effects from nonlinearities and external disturbances.Firstly,this paper introduces a contour error model based on the T-C coordinate transformation and demonstrates the validity of the model.A mathematical model is established based on characteristics and structure of the system.Considering the matched and mismatched disturbances in the system,a contour controller based on the sliding mode control and generalized proportional integral observer is proposed,in which nonlinearites and external disturbances are regarded as lumped disturbances.The disturbances are observed by generalized proportional integral observers and compensated in the controller.The simulations and experimental results demonstrate the superiority and effectiveness of the controller.The switching gains of the controller are reduced and the chattering phenomenon is suppressed.In order to improve the convergence speed and the machining accuracy of the system,a composite contour control algorithm based on the non-singular terminal sliding mode control and finite-time disturbance observer is proposed in this paper.This controller realizes the finitetime control of the contour error,increases the convergence speed of the contour error and makes the actual operating point closer to the desired trajectory.Simulation and experiments show that the composite control method has higher tracking accuracy and contour accuracy than the controller based on the sliding mode control and generalized proportional integral observer.Friction shows strong nonlinearity at a low speed,which will have a great impact on the accuracy of the contour machining.In order to eliminate the influence of friction in the system,this paper introduces a RBF neural network to fit the friction model and compensate it in the controller.A finite-time disturbance observer is designed for estimating the fitting error and disturbances.The effectiveness of the fitting method is demonstrated by simulations and experiments.Compared with the controller without friction compensation,the contour tracking performance of the composite controller based on friction compensation is significantly improved.