Research On Modeling And Compensation Of Friction And Temperature Change Interference Of Servo System

Nonlinear Friction exists in the servo system. Temperature changes not only affect friction, but also cause to produce thermal deformation error, thus seriously affect control and positioning accuracy of servo system. With wider use of servo system, it requires much higher accuracy. Reduction or elimination errors in the servo system caused by changes in friction and temperature have become a critical issue in the realization of servo system. In this paper, aiming at this problem, combined theoretical analysis with experimental analysis, friction that reflects influence of temperature and modeling and compensation of axial thermal deformation of screw are deeply researched separately.First, modeling and identification of friction model that reflect temperature changes are accomplished. Backstepping method based on state error is used to separate and obtain torque ripple and friction moment in the servo system; spectral analysis, least squares and other methods are adopted in the identification of torque ripple, and motion controller is used in the compensation; genetic algorithm is used in the precise identification of dynamic and static parameters in the custom LuGre model; viscous friction in the custom LuGre model is corrected according to experiments, making friction in the servo system is accurately reflected even in high speed; influence on the friction by temperature changes is studied, and based on temperature observation on the key point, method of applying neural network to the modeling of static parameter of LuGre friction model is proposed, thus introducing temperature to the friction model, and friction model that reflects temperature changes is built.Then, friction compensation strategy of servo system based on the error correction model is researched. On the one hand, control method of feedforward PD constant friction compensation is adopted, and control accuracy of servo system is improved; on the other hand, aiming at parameter changes of friction model in the servo system, uncertain nonlinear modeling error and other disturbances, adaptive backstepping sliding mode friction compensation method based on the backstepping design is proposed, design method of compensation controllers is provided, and asymptotic stability is verified. Adaptability and robustness of this method is proved by the tests, effectively improve tracking accuracy of servo system. Last, axial thermal deformation error of screw caused by temperature variation is analyzed and modeled. Geometric errors such as pitch error and backlash are compensated;thermal characteristics of ball screw assembly is analyzed, and come to a conclusion that thermal deformation not only determined by the state of internal heat source at that time, but also affected by the previous state; method that use self-recurrent wavelet neural network (SRWNN) is presented to model axial thermal deformation error of screw, acquiring good modeling effect, and effectiveness of the model is verified by experiments.