Research On Position Control Of Pneumatic Servo Welding Gun System

Spot welding gun is the key equipment of automobile body-in-white welding process.The welding quality of body-in-white directly affects the quality of automobile body.With the prosperity of automobile market,the traditional pneumatic welding gun has been unable to meet the requirements of body-in-white welding because of its poor control precision and short life.In this dissertation,the position control of pneumatic servo welding gun system is studied.Firstly,the pneumatic loop of pneumatic servo welding gun is designed,and the mathematical model of valve controlled cylinder link of pneumatic servo system is deduced in detail.The transfer function of the system is calculated according to the relevant parameters of the research object,and the frequency characteristics of the transfer function are analyzed by MATLAB to judge the performance of the system.The analysis results show that the system is stable but the dynamic performance is poor,so it is necessary to add a controller to improve the dynamic performance of the system.The PID controller,fuzzy PID controller and fractional PI~?D~?controller are designed respectively,in which the fractional PI~?D~?controller uses the stability margin method to adjust the parameters,and the PID controller uses the critical proportional method and the stability margin method to adjust the parameters.The simulation block diagrams of the three controllers are built in Simulink,and the dynamic response curves of the three controllers to the unit step signal are compared.the simulation results show that the fractional PI~?D~?controller has a good control effect on the pneumatic servo system.The system has good signal tracking performance,strong anti-interference ability and strong robustness.The influence of the five parameters of the fractional PI~?D~?controller on the system performance is analyzed,the change of the five parameters in a small range has little effect on the system.It is further proved that the fractional PI~?D~?controller makes the system have strong robustness.The correctness of the mathematical model of the pneumatic servo system and the rationality of the research based on the mathematical model are verified by the combined simulation with AMESim and Simulink software.Finally,the positioning accuracy and repeated positioning accuracy of pneumatic servo welding gun controlled by fractional PI~?D~?are investigated experimentally.the experimental results show that the positioning accuracy and repeated positioning accuracy of pneumatic servo welding gun controlled by fractional PI~?D~??are0.5 mm.