Research On The Manipulator Joint Driven By Pneumatic Muscle

Pneumatic muscles, as a new type of actuator, have many advantages, such as simple construction, small volume, safe and flexible, and highest power/weight ratio, which has been given attention by scholars recently. Focusing on the pneumatic muscle, simplified and improved static and dynamic mathematic models have been developed based on the current theoretical approaches in the dissertation. And also the mathematic models are applied to the manipulator joint driven by pneumatic muscle and spring. After analyzed the quasi-static and dynamic characteristics of the control system, a global sliding model controller strategy is proposed using the variable structure control theory. The simulation and the experimental results show that the closed-loop tracking performance of the controller is well, and the controller is robust to the external interference and parametric variation which can achieve satisfied results.Firstly, on the basis of the former idealized static physical model of pneumatic muscle, effective coefficients to volume caused by rubber elasticity, the shape at both ends of the rubber tube, and the friction between rubber tube and braided mesh shell is calculated. The simplified and improved static and dynamic mathematic model is given then. As a digital valve, the high-speed on-off solenoid valves control the air flow in and out of the pneumatic muscles in the form of duty ratio generated by PWM (Pulse-modulated signal). The variation in charge and discharge cause the pressure changes in the cavity of pneumatic muscle, which produces the rotation of the elbow angle. At last, considering the pneumatic muscle as a variable cross-section air cylinder, the dynamic differential equation of pneumatic muscle is modeled combined with the gas-flow equation, energy conservation equation, and dynamic equation of the system.Secondly, according to the operating principle of the manipulator joint driven by the single pneumatic muscle and spring, the thesis develops the joint's static mathematical model, and finds out how the charged pressure and spring stiffness influence the elbow angle. Making use of the former dynamic differential equation of the pneumatic muscle and the dynamic model of the joint, the state equations are built with the rotation angle, angular velocity and charged pressure as the state vector, and also some parameters are analyzed on the influence of the output angle. All these can make us to take effective method to design suitable controller so as to obtain the high precision and the rapidity of the joint angle. Because of the nonlinear of the pneumatic muscle, it's difficult to get the accurate mathematical model of the system; meanwhile the state equations are coupled. To make it easy to design the controller, the state equations are simplified, and changed to a 3-order nonlinear system.At last, against the nonlinear of the servo-system and difficulty to get the accurate model, the global sliding model control strategy is used to control the pneumatic positional servo-system, utilizing robustness and insensitivity to the uncertain mathematical model of the system and external disturbance of the sliding model variable structure control theory. Tracking error and steady-state error in the different simulation parameters are also analyzed. The experimental results show that the controller can improve the dynamic characteristic of the system, respond smoothly and produce small overshoot. The controller is suitable for the study of the position servo control on pneumatic artificial muscle joint.