Analysis And Compensation For The Friction In Hydraulic Servo Systems

The main purpose of this paper is to study the friction force in hydraulic position servo system, especially when it is running at low velocity state, and to make effort to compensate it. According to the elaborate analysis on friction at home and abroad, a dynamic friction compensation method is proposed to compensate the system's friction force at low velocity. A dynamic friction model is build and a friction observer is designed for ordinary position servo system. This friction model and compensation measure is effective, which is testified by doing experiment and simulation. Firstly, this paper studies every component of the servo system to improve the performance at low speed. From the analysis results, we learned that the main influence factor is friction force. Therefore, in order to improve the system low speed performance, it is necessary to compensate the friction force. Based on well knowing the friction mechanism, this paper absorbs advanced research results in this field, summarizes the strongpoint and insufficiency of traditional friction compensation methods, and proposes a dynamic friction compensation method according to a new friction model (LuGre friction model).Secondly, this paper emphasizes how to apply this new friction model to practical valve controlled cylinder position servo system and realize the dynamic friction compensation. The paper designs the compensation law and uses the MATLAB/Simulink tools to testify the compensation effect. Because the friction force mainly influences the track precision and the orientation precision of the servo system, it should consider these two targets changes between before and after compensation. Low-velocity ramp signal and step signal were chosen as simulation test signal. The simulation results indicate this new friction model has good compensation effects and can compensate friction force dynamically. This method provides an efficient way to design high precision, low speed electro-hydraulic servo system.Finally, in order to realize real time control, computer data acquisition and control program are designed. Using Windows 98 as its O.S., the control software is developed by using Visual C++ language. The results show that the software has strong application value and its interface is interactive and easy to operate. The experiment results indicate this friction compensation method can effectively compensate the friction and greatly improve the system character.