| The low velocity smooth properties of DC PWM servo system affect the precision of the tracking system. With the rapid progress of precision tracking techniques, the performance and precision of tracking system is needed to be increased, and corresponds to improve the precision of the DC PWM servo system. But the improvement of servo system is limited to the existence of disturbing moment, for example nonlinear friction moment. Therefore, develop high performance PWM power amplifier and study on friction analysis and compensation is of important application value to design a precision DC servo system with simple structure and quality. Taking the 718 turntable as an object, the paper focuses on the effect of the nonlinear friction moment, makes theoretical analysis on the influences due to friction. The friction compensation based on the LuGre friction model is researched. Designed the PWM power amplifier based on the IPM, analyzed the influence of PWM power amplifier on the low velocity properties of servo system by experiment. At last, the friction compensation based on the LuGre model is verified on the 718 turntable. Against the effect of low velocity performance due to nonlinear friction, nonsmooth Lyapunov stability theory and analysis are proposed to study stability of servo system with friction. The sufficient condition with which the system will never occur stick-slip is given in theory. A recursive estimation method is presented on the condition of the model parameters are unknown; the LuGre friction observer is designed. Basing on the LuGre friction model, an adaptive control system is designed first according to adaptive control theory. Eventually, utilizing the friction moment and friction model parameters which are estimated before, the simulation of two friction compensation method is accomplished. The simulation results make know the nonlinear friction compensation can improve the low velocity property. Considering the 718 turntable as subject investigated, the main property parameters are measured. Realized the design of LuGre friction observer and LuGre model adaptive controller with C language, compensated the effect of friction, the output curve of system is presented. The output characteristic of system which adopted different compensation methods is compared. The experiment results show that he LuGre model adaptive friction compensation can restrain the effect of nonlinear friction, and improve the low velocity performance of DC PWM servo system. Finally, the work principle of PWM power amplifier and the magnitude of armature current are analyzed. The slight vibration prosperity of motor in DC PWM servo system, and the effect of dead-zone of PWM control signal on the low velocity properties are discussed. The experiment about the influence of PWM power amplifier on the low velocity properties is fulfilled on the 718 turntable, the result indicates the bipolar PWM can improve the low velocity performance of servo system.
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