Abstract
This paper examines the availability of a modern control theory to the pneumatic servo system implemented with a pneumatic cylinder and electro-pneumatic proportional control valves. Due to the low stiffness from air compressibility, a pneumatic system is limited in a response speed and very sensitive to the variation of frictions or load forces. These difficulties may be overcome with the high gain control or the control law including an integral action. On the other hand, the available electro-pneumatic control valves involve a considerable operating delay time, which makes such controls more difficult.
In this study, to compensate the valve delay, which is formulated as an input time-delay in the discrete state equation, for which the 0-type and 1-type optimal servo systems are designed. Experiments show that the control system design considering the valve delay makes the 1-type servo system satisfactory with both stability and response speed, so that the advanced position control performance can be obtained independently of load forces.
The proposed servo systems require only a position sensor, and estimate other state variables by the observer. Moreover, the used computer has so sufficient computational ability that it can also control some servo systems simultaneously to lower the cost for one cylinder. Consequently; it proves that the application of a modern control theory can fairly improve the control performance of pneumatic servos without losing its simplicity and low cost advantages.
