Reinterpretation of PDD2 compensator embedded in position control for pneumatic stage

摘要

PDD~(2) (proportional + derivative + second derivative) compensator has been standardly used for position control of the pneumatic stage. This compensator is based on the integral characteristics of a pneumatic system composed of pipes, servo valves, and pneumatic cylinders. At this time, since the output of this compensator is integrated through the pneumatic system, PID control of the position is possible. However, the positioning of the pneumatic stage is slower than that of the electromagnetic actuators such as a linear and a ball screw stages. Generally, when either the controlled object or the compensator has a slow response, the response of the control system becomes slow. In the previous studies, the pneumatic stage itself, which is the controlled object, was focused on. Local feedback applied to the pneumatic and mechanical systems realized high-speed positioning. However, the influence on the positioning response using PDD~(2) compensator, which forms the framework of the position control, has not been considered. Therefore, this note focuses on the structure of PDD~(2) compensator. Here, the characteristics of this compensator are reinterpreted. Specifically, it is shown that a slow response cannot be avoided intrinsically due to the structure of this compensator. Furthermore, modified PDD~(2) compensator with improved slow response is proposed.