Positioning control of a pneumatic stage under different pipe length: Performance improvement of PDD² control and suppression of flow disturbance

In this study, we consider the positioning of a pneumatic stage in order to compensate effects of different length of pipes, which connect servo valves and cylinders. Since, in industrial scenes, it is difficult to use pipes of the same length due to the structure of industries, the length of each pipe is often different. In this case, the characteristic of the pneumatic system, which consists of the pipes, servo valves, and chambers, changes in accordance with the pipe length. It leads to two issues: The first one is that the performance of proportional-derivative-double derivative (PDD²) control, which is effective for the control of pneumatic actuators, is degraded. To overcome this issue, the parameter of a pre-compensator for the PDD² control is tuned. The suitable value of this tuned parameter increases with the length of the pipes. The second one is that the effects of flow disturbance increase due to the different pipe length. When the length of the pipes is not same, it is probable that the magnitude of flow disturbance transmitted to each pipe is different. For this reason, multiple flow disturbance observers (FDOBs) are implemented in a control system. Experimental results show that the repeatability of the positioning is improved by using the FDOBs.