A study of implementation of model following control for a pneumatic stage

Abstract

This paper considers the performance improvement of pneumatic stage positioning. The pneumatic system, which consists of air cylinders, servo valves, and pipes supplying compressed air to a pneumatic stage, have parameter variation due to mainly air compressibility. It leads to low positioning repeatability. To compensate for this parameter variation, model following control (MFC) is employed for the pneumatic system. One of authors has previously shown the effectiveness of MFC. However, how to select desired model to follow and controller used for MFC (called “the model following controller”) is not considered sufficiently. Then this paper considers appropriate model and the model following controller from the viewpoint of transfer function. As a result of considerations, it is found that the model cannot be selected freely, as represented by reference model of model matching two degrees-of-freedom control system, but rather should be just equal to the pneumatic system. Furthermore, it is also found that a PID controller is better than a PI as the model following controller so as to improve transient response of MFC. Validity of the proposed model and model following controller are presented by pole-zero loci and experimental results. The effectiveness of MFC with both proposed model and model following controller is shown by results of repeated positioning.

Keywords

• model following control
• motion control
• pdd2 control
• pneumatic equipment
• positioning