Modeling and controller design for pneumatic artificial muscle for ankle-foot orthotic device

Abstract

In the present era Electric motors are most commonly used actuators for various robotic and bio-robotic applications. However, the functioning of electric motor is not similar to human skeletal muscles. Also, the electric motors are prone to harm human beings in case of failure. Hence, the present work has focused on exploring a bio-inspired actuator, which functions similar to human skeletal muscles and is safe for human beings. The literature review has revealed that such an actuator is pneumatic artificial muscle (PAM). In the present work the researchers have focused on developing an efficient model and control strategy for PAM in order to use it for bio-robotic applications. An experimental setup has been prepared to analyze the behavior of PAM for different speeds of operation and different loading conditions during inflation/ deflation. Based on the experimental datasets an experimental model of PAM and Proportional Pressure Regulator (PPR) has been developed using polynomial curve fitting tool of MATLAB. Then a switched mode feedback PID control strategy has been developed for PAM which takes care for the hysteresis behavior of PAM. The control strategy has been simulated to achieve the trajectory angle tracking of ankle joint during the complete gait cycle. The simulation of the proposed control strategy with the developed model has shown that the proposed approach works fairly well and the error in the ankle joint movement could be limited in the range of-0.8° to 0.6° for the complete gait cycle. The result obtained in the present study is similar to the results as reported in the literature. However, this could be achieved with less system complexity using simpler modeling technique and “switched mode feedback PID controller”, which has not been reported by any researcher till date.