Experimental Comparisons of Sliding Mode Controlled Pneumatic Muscle and Cylinder Actuators

Pneumatic muscle actuators offer a higher force-to-weight ratio compared to traditional cylinder actuators, and introduce stick-slip-free operation that offers an interesting option for positioning systems. Despite several advantages, pneumatic muscle actuators are commonly avoided in industrial applications, mainly due to rather different working principles. Due to the highly nonlinear characteristics of the muscle actuator and pneumatic system, a reliable control strategy is required. Although muscle actuators are widely studied, the literature lacks detailed studies where the performance for servo systems is compared with traditional pneumatic cylinders. In this paper, a pneumatic servo actuation system is compared with a traditional cylinder actuator. As the overall system dynamics are highly nonlinear and not well defined, a sliding mode control (SMC) strategy is chosen for the control action. In order to improve the tracking performance, an SMC strategy with an integral action (SMCI) is also implemented. The control algorithms are experimentally applied on the pneumatic muscle and the cylinder actuator, for the purposes of position tracking. The robustness of the systems are verified and compared by varying the applied loads.