Modeling And Control For Flexible Joint Driven By Pneumatic Muscle

Pneumatic artificial muscles,as a new type of actuator,have many advantages,such as simple construction,small volume,safety and flexibility,and high power/weight ratio,which has been given attention by scholars recently.Focusing on the pneumatic muscle,the static model and a new phenomenological model consisting of a contractile(force-generating)element,spring element,and damping element in parallel have been developed based on the current theoretical approaches in the thesis.And also the mathematic models are applied to the flexible joint driven by pneumatic muscle.After analyzing the characteristics of the flexible joint control system,the PID controller and the sliding mode controller are designed.The simulation and the experimental results have demonstrated that the model and the controller can achieve the desired performance in tracking a desired trajectory.Firstly,the idealized static physical model of pneumatic muscle built by Chou is analyzed.Then regarding pneumatic artificial muscle as equivalent function area cylinder,the dynamic energy-balance equation of pneumatic artificial muscle is studied.According to the pneumatic artificial muscle dynamic performance analysis,we identify the parameters of three-element model by experiments.Secondly,we consider a flexible joint driven by two antagonistic pneumatic muscles and develop the flexible joint's static mathematical model,analyzing the influence of charged pressure on elbow angle.According to the three-element model and the dynamic equation of joint,the state equation of angle and angle velocity are established.The proportional control valves control the air flow in and out of the pneumatic muscles,which produces the rotation of the elbow angle.According to the characteristics of the flexible joint,an experimental platform is set up to control the angle of the flexible joint,and the components are selected for the experiment.Finally,the PID and sliding mode controller are designed for the flexible joint and the simulation of flexible joint control is built by combining the mathematical models.The simulation and experimental results show that the PID controller cannot get a good dynamic performance,however,the sliding mode controller can improve the dynamic characteristic of the system,respond smoothly.The sliding mode controller is suitable for the flexible joint.