Study Of Pneumatic Servo Trajectory Tracking Control Based On Proportional Valve

With the distinctive advantages such as the energy-saving, non-pollution,simple structure,large power output,relatively lower price etc.,the pneumatic servo control technology has attracted more and more attention and has been applied widely as well.At present most of the pneumatic servo technologies used in industry are aimed to the point-to-point position control,while the application of pneumatic servo system with continuous trajectory tracking control is not so wide.As a result it limits the development of pneumatic technology to a large degree. To this point,the article aims at finding the proper control strategy,and obtaining the ideal pneumatic servo system with well trajectory tracking effect.Firstly the present home and abroad development situation of pneumatic servo with trajectory tracking is analyzed.According to the feature that the friction force of cylinder is the main factor which has influence on pneumatic position control system,a experimental analysis on friction force of DGPL series non-rod cylinder under different pressures and different loads is done,and thereby the mathematical model of friction force is built.Secondly though the theoretical analysis,the mathematical model of pneumatic servo system based on proportional valve is deduced,which takes the MPYE series proportional valve as a example,and adopts the classical control method-PID control which uses the Ziegler-Niehols parameter setting method to make parameter setting on PID controller to make the trajectory tracking.Then the modeling and simulating for the system using Matlab/Simulink software is made,which proves the correctness of the mathematical model.The trajectory tracking simulation of step signal and sine signal to the system is also made.But because of the effect of nonlinear caused by the pneumatic servo system itself,it is different to obtain good control accuracy using PID control. Lastly the sliding mode variable structure control based on friction compensation is proposed according to the various shortages of PID controller as well as the delay of gas pressure response caused by the gas compressibility and the effect to the system of the cylinder nonlinear friction.By using the smooth curve function s/|s|+ψinstead of sign function sgn(·),the occurrence of system chattering is restricted.This method effectively solves the buffeting problem of sliding mode variable structure.The Matlab simulation experiment is done which makes trajectory tracking to the step signal,sine signal and round plane for the system.The simulation results show that the control algorithm outperforms the PID control.The tracking accuracy is improved and it has very strong robustness.