Research On Robot Joint Control Driven By Pneumatic Artificial Muscles

As robots have been studied in the fields of bionics,service and rehabilitative medicine,people's demands for the weight,flexibility and safety of the drives have also been improved.Pneumatic artificial muscle has been paid much attentions by researchers at home and abroad due to its advantages of light weight,large driving force and similar characteristics to human muscles.In this paper,the robotic joint driven by pneumatic artificial muscle was studied.Through the combination of theoretical analysis and experimental research,the static and dynamic mathematical models of pneumatic artificial muscle were established and applied to the robotic joint.Based on the research of the dynamic characteristics of the robotic joint control system driven by the pneumatic artificial muscles,a fuzzy PID controller was designed based on the fuzzy control theory and PID control theory,and compared with the conventional PID controller,the simulation analysis was carried out.Firstly,focusing on the main factors that restricting the contractile force of pneumatic artificial muscle,on the basis of the ideal model,the functional relationship between driving force,pressure,and contraction displacement was established by the analytic method.Through the experimental and simulation studies,the mathematical model was verified and the static characteristics of robotic joint driver were analyzed.Based on the experimental data,the parameters of the model were identified and a modified model of the pneumatic artificial muscle was established,which improved the accuracy of the original model.Secondly,from the aspects of mechanical structure,pneumatic circuit and the hardware of control system,a robotic joint test-bed was designed.Based on the modified model of pneumatic artificial muscles,a static mathematical model of pneumatic joints was established,and the correspondence between joint rotation angles and pressure difference in two pneumatic artificial muscle chambers was obtained.Combining the flow equation of the highspeed switching valve,the dynamic characteristic equation of the pneumatic artificial muscle and the dynamic equation of the joint,a dynamic model of the robotic joint system was established.Thirdly,based on the fuzzy control theory which did not require accurate mathematical model of the controlled system,a fuzzy PID control strategy was proposed for the robotic joint control system driven by the pneumatic artificial muscles.Comparison of the computer simulations found that the conventional PID controller had slow response speed,large overshoot and long adjustment time after being affected by interference signals.Compared with the conventional PID controller,the fuzzy PID controller had smaller overshoot,faster step response and stronger robustness and was suitable for the control of robotic joints driven by pneumatic artificial muscles.