Research On The Position Control Strategy Of Pneumatic Muscle Actuator(PMA) And The PMA-actuated Parallel Robot

Pneumatic muscle actuators (PMAs) are new type of actuators which have the advantages of inherent compliance, flexility, high power/weight ratios, high power/volume ratios, light weight and cheap compared to traditional actuators. They are appropriated for bionic robot and rehabilitation robot. According to statistics, the number of patients who lost physical capabilities has been increased obviously while the therapists are lack of. Rehabilitation robot can play the role of therapists. It restores and enhances the patients’limb neuron by moving the affected limb repetitively. Moreover, parallel robot possesses the advantages of heavy-load capability and small accumulative error. Applying PMAs to parallel robot for rehabilitation is a beneficial attempt.Meanwhile, PMAs are of high non-linearity and time varying parameters. It is hard to control the position of PMAs with a high precision, thus bringing difficulty for the application of them. To address these issues, this paper particularly researched the model and control strategies of PMAs. By combining PMAs with parallel robot, this paper designed a PMA-driven parallel robot and analyzed the characteristics of this robot.The research contents included:(1) Considering the physical characteristics of PMA, a new model of PMA which consisted of driving element, hysteresis element and rubber elasticity element was established and verified by experiment.(2) Based on the proposed model of PMA, a new control strategy was proposed. The fuzzy logic control was tested and it shown good ability of overcoming the crawl of PMA. The model of PMA was used for compensation to feed forward to the output of the self-organize fuzzy controller and it obviously narrow the difference between the real trajectory and the desired trajectory. A self-organize mechanism was used to improve the robustness of the fuzzy controller. The research of control strategy for single PMA laid solid foundation for the control of PMA-actuated parallel robot.(3) Based on the requirement of ankle rehabilitation, a two-DOF parallel robot actuated by three PMAs was proposed and the kinematics, dynamics, working-space and maneuverability of this robot was researched and verified.