Trajectory Control of Pneumatic Servo Table with Air Bearing

Abstract

This paper proposes a trajectory control design for a pneumatic servo table system. The control design takes into consideration the dynamics of the pneumatic actuator, connected pipeline and servo valve. The system is mainly composed of a pneumatic actuator, high-performance pneumatic servo valves and pipelines. The pneumatic actuator utilizes a pneumatic cylinder with air bearing. The servo valve, which has high dynamics up to 300 Hz, is connected to the pneumatic actuator by pipelines. A linear model which takes into consideration the dynamics of the pipeline and servo valve is designed to simulate the system. Experiment results suggest that with 7thorder control model the system can be accurately represented. However, a low-dimensional model is necessary for practical use. The analysis shows that in the pole loci of the 7thorder model, two poles are much farther from the imaginary axis than are the other five poles. Therefore, the model can be reduced to one of the 5thorder. By comparing the simulation and experiment results, we confirm that the 5thorder model can also match the system well. Based on this result, a 5thorder feed forward has been designed. When a curve which can be derived five times is inputted, the experiment results show that the maximum trajectory error has been reduced by 20 µm.