Improved tracking accuracy of a pneumatic actuator on entire piston stroke by a modified fuzzy-PWM controller

Abstract

Position control of the piston through whole stroke of the pneumatic cylinder can lead to better performance of the actuator in various processes. In this paper, by dynamic and thermodynamic modeling analysis, a significant difference in dynamic behavior of the pneumatic actuators through whole piston stroke is revealed that deteriorate the control performance at both ends of the stroke, when non-model-based controllers with fixed structure and constant gains are used. However, in some systems, non-model-based controllers are preferred because of their simplicity in designing and application. Thus, a PD-structured fuzzy-pulse width modulation controller (MF-PWM) that modified by applying the feedback of the piston position as the third input to the control block is developed to improve the tracking accuracy through the border ranges of the stroke. The pneumatic actuator has been applied for lower limb rehabilitation. Hence, to evaluate the developed controller performance, the tracking accuracies of the experimental results of MF-PWM and usual fuzzy-PWM controllers were compared, while the pneumatic actuator interacts with different users. The experimental results demonstrated performance improvement of the MF-PWM controller.