Research On An Adaptive Sliding Mode Control Strategy For Electro-hydraulic Position Servo System

Electro-hydraulic servo system has many unique advantages,such as convenient signal detection,correction and amplification,easy to realize remote operation,easy to be integrated with hydraulic components with fast response and big anti load stiffness and so on.According to its output,electrohydraulic servo system can be divided into position servo system,speed servo system,force servo system and so on.Electro-hydraulic position servo system is one of the most basic and most commonly used hydraulic servo system,whose main task is to achieve timely and precise tracking.Electro-hydraulic position servo system has been widely used in different military and civil fields,such as thickness control of rolling mill,missile position control,aircraft control,copying machine,CNC machine tools,etc.However,the electro-hydraulic position servo system is a system with severe uncertainty,complex working environment and task and it is quite common to see parameter changes and external interferences in electrohydraulic position servo systems.Secondly,the electro-hydraulic position servo system has high requirements on the frequency band and the tracking precision,and the influence of nonlinearity cannot be ignored under the condition of high precision and fast tracking.These characteristics make the design of electro-hydraulic servo control system a great challenge,and it is difficult to achieve satisfactory control effect only using the traditional control algorithm.Therefore,how to realize the robust control of the electro-hydraulic position servo system has become an important task,and it is also of great significance.In this paper,to deal with nonlinearity as well as parameters changes and external interferences,an adaptive sliding mode control strategy is proposed for the position tracking control of electro-hydraulic position servo system.In this strategy,fuzzy inference method is used to adjust the thickness of the boundary layer,so as to eliminate the chattering phenomenon in the variable structure control.Simulation and experimental results show that the proposed control strategy not only can improve the tracking accuracy,but also has strong robustness,compared with traditional control strategies.The main research work is as follows:(1)The composition of electro-hydraulic position servo system and development status and development trend of electro-hydraulic servo valve are studied and requirements on control strategies for electro-hydraulic position servo system are listed according to its characteristics.Then,the basic principle,chattering phenomenon and its elimination of the sliding mode variable structure control method are summarized.Besides,the application status of sliding mode variable structure control method in the electro-hydraulic position servo system is discussed in this paper.(2)According to the specific needs of the experiment,the key components of the system such as electro-hydraulic servo valve,hydraulic cylinder,displacement sensor and so on are selected,and the complete experiment platform is built.(3)Transfer function and its simplified forms of valve controlled system are obtained using transfer function method,and then based on the mathematical model of valve controlled system,the mathematical model of electro-hydraulic position servo system is deduced and obtained.Furthermore,the performance of the system is analyzed using the bode diagram method according to its mathematical model.In addition,the state space mathematical model of the electro-hydraulic position servo system is derived,according to the three equations of electro-hydraulic position servo system,namely,dynamic equilibrium equation,flow continuity equation of hydraulic cylinder and flow equation of servo valve.(4)PID controller,conventional sliding mode controller and adaptive sliding mode controller are designed respectively for the electro-hydraulic position servo system in this paper.Then,the specific control algorithms are realized in Simulink,and the control performances of the three control strategies are compared and analyzed in the form of AMESim/Simulink joint simulation.(5)The hardware control system of the electro-hydraulic position system is designed.Then,according to designed controllers and simulation parameters,the computer control algorithm is programmed in LabVIEW to verify the simulation results.The simulation and experiment results show that the proposed conventional sliding mode controller can significantly improve the tracking accuracy of the electro-hydraulic position servo system compared to the traditional controllers,and the proposed adaptive sliding mode controller not only can further improve the tracking accuracy,but also greatly reduce the chattering of the system and improve the stability of the system.