Modeling And Control Of Servo System With Friction

With the widely use of servo system, high precision servo system control has become a hot topic in motion control. A type of radar's high precision angular tracking servo system (RHPATSS) can be modeled as a servo system with friction. It is known that friction element is an important nonlinear factor contained in servo systems and has great negative effect on improvement of system control accuracy. It is also noted that modeling, identification and control of servo systems became very difficult due to the nonlinearity arising in friction element. In this paper, according to the requirement of control of RHPATSS, the modeling, identification, friction compensation and anti-wind up problem of a class of servo systems with friction have been studied.The dissertation is organized as follows. The modeling and parameter identification problem of angle tracking DC servo system with friction are analyzed in the first part of this paper. Firstly, the mathematical model of the system is obtained by physical property analysis of the system. Secondly, a two-step parameter identification method is used in parameters identification of the system. The first step is measuring the Stribeck curves and using the genetic algorithm to obtain the static part of LuGre friction model parameters. The second step is reducing the system to a second-order system according to the low-speed characteristics of the friction model and obtaining the dynamic part of LuGre friction model parameters and system inertia based on input-output data by using system identification theory, thus to complete the identification procedure. Thirdly, the simulation results are given to show the effectiveness of the proposed parameter identification method.The second part of this paper is the system analysis and controller design. Firstly, the reason of the "stick-slip" phenomena is analyzed, and it is shown that the PID controller can not achieve stability control. Secondly, the feedforward PID fixed friction compensation controller is designed. Thirdly, a modified LuGre friction model is proposed and . Then, an adaptive backstepping friction compensation with anti-windup controller is designed with consideration of the system input saturation. Finally, based on Lyapunov stability theory, it is proved that the three controllers can guarantee that the closed-loop systems are stable. And the simulation results show that the feedforward PID controller can reduce the system "stick-slip" motion and improve the tracking accuracy but with less robustness. The adaptive backstepping friction compensation based on modified LuGre friction model not only eliminate the "stick-slip" phenomenon and significantly improve the tracking accuracy,but also gain strong robustness. The adaptive backstepping friction compensation with anti-windup controller ensures the tracking accuracy with the emergence of input saturation.