Research On Pneumatic Muscle Actuator Position Servo System And Its Application

The main objective of this dissertation is to report research on pneumatic muscle actuator(PMA), which has been given attention by scholars as a new type of pneumatic actuatorrecently. In this dissertation, an improved static and dynamic mathematic model of PMA wasdeveloped by means of theoretic analysis and verified through experiment, and according tothe characteristics of PMA system, a fuzzy variable structure control (FVSC) method wasdesigned and also applied to control the position of a novel 3-DOF parallel manipulatorequipped with PMAs working as driver. Firstly, a discussion was made to analyze the reasons, which may be responsible for thegreat discrepancy between the idealized static mathematic model and the experimental results.Based on the discussion, a new improved static mathematic mode of PMA was developedconsidering the rubber elasticity and the friction between rubber tube and braided mesh shell,and a new concept was presented, which regards PMA as variable piston area pneumaticcylinder with elastic load. Two types of actuators were tested to verify the model, and thestatic characteristics of PMAs were studied by computer simulation and experiment. Secondly, the PMA system was studied as a pneumatic transmission system and anonlinear dynamic model of PMA system was presented easily according to the new conceptand the dynamic model of pneumatic cylinder. To facilitate research works, the workingprocess of PMA system is divided into four successive processes, 'isometric inflation','contractive inflation', 'extended disinflation' and 'isometric disinflation'. At the end of thispart, computer simulation and experiment were applied to discuss the dynamic characteristicsof two types of PMA system. Thirdly, due to the complex nonlinear dynamics of PMA and difficult in obtainingaccurate mathematic model, classic control method is not suitable for the system. A FVSCmethod was presented to control the position of PMA servo system. The FVSC controller isintergrated with two layers of sliding surface. The result of simulation and experimentcompared with conventional variable structure control (CVSC) method shows that FVSC canimprove the static and dynamic behavior of the system effectively and CVSC is not workablebecause of the undesirable "chattering" of control input and nonideal performance. The two -III -types of PMA control system have stronger robustness, quicker tracking and higher accuracy.The steady-errors are below ±0.2mm and ±0.3mm respectively, and even though mass orsupply pressure is varied the steady-errors are within ±0.3mm and ±0.5mm respectively. Finally, a novel 3-DOF parallel manipulator equipped with PMAs was constructed byrequest of a kind of underwater-simulated device, which has only 3 rotational degrees offreedom. PMAs are acted as driver because of its advantages of being compact, airproof andhaving the ability to work in adverse environmental conditions. On the basis of analyzingkinematics and dynamics of the parallel manipulator, a FVSC controller for the manipulatorwas designed. Then experiment of the parallel manipulator trajectory tracking was carried out,and the result demonstrates that the novel 3-DOF parallel manipulator using PMAs isappropriate and FVSC method is suitable for the parallel manipulator. The work is useful forthe application in practice of PMA.