Control System Design of a Pneumatic Servo System

Pneumatic servo systems are applied in several industrial applications and have also been studied extensively for the purposes of compensating the nonlinearity of pneumatic servo systems and improving the controllability with robust control. In their control system design, the transfer function of a pneumatic servo system has been a third-order time lag system, based on the assumption that servo valve dynamics is negligible because it is sufficiently faster than cylinder dynamics. However, the characteristic of a servo valve greatly influences the dynamic characteristic of the pneumatic servo and should be taken into account in the control system design. In this research, a new method of control system design, which deals with the pneumatic servo system as a fifth-order time lag system including a second-order time lag system of a servo valve, has been proposed. The experiment shows that the proposed method is effective. As a result, we can decide all of the control parameters including the proportional gain without trial and error. The obtained proportional gain can be larger, so that the performance of a pneumatic servo has been improved.