QFT synthesis of a position controller for a pneumatic actuator in the presence of worst-case persistent disturbances

Quantitative feedback theory (QFT) is employed in this paper to design a simple and effective position controller for a typical industrial pneumatic actuator. An emphasis is placed on minimizing the effects of load disturbances. The QFT control law is designed to give the best attenuation of the prescribed worst-case persistent load disturbance in spite of practical limitations on the achievable closed-loop performance and in the presence of other design constraints including closed-loop tracking and stability. The efficacy of the control law is verified in simulations and the guaranteed upper bound on the position error due to the worst-case persistent disturbing load is determined. This paper also highlights some of the issues related to QFT design for pneumatic actuators in the presence of load disturbances including dry friction that, to the best of the authors´ knowledge, have not been adequately detailed elsewhere