Trajectory control of pneumatic servo table with air bearing

In this paper, the trajectory control design of the pneumatic servo table considering the dynamics of pipelines and servo valve is proposed. The table is mainly composed by a pneumatic actuator, the high-performance pneumatic servo valve and pipelines. The pneumatic actuator utilizes a pneumatic cylinder with air bearings. This servo valve, with high dynamics up to 300Hz, is connected with the pneumatic actuator by pipelines. The whole system is pneumatically driven, it has advantages like low heat generation and non-magnetic, which are suitable for precise positioning. A linear model considering the dynamics of pipelines and the servo valve is designed to simulate the system. Compared with experimental results, it is found that with 7^th order linear control model, the discrepancy between experimental and simulation results became much smaller than the 3^rd order model was used. However, a low dimensional model is necessary for practical use. Since there are two poles which are much further from imaginary axis compared with other five poles in the pole loci of the 7^th order model, the model's order can be reduced into 5^th. By comparing simulation with experimental results, we found that the 5^th order model can also match with the real system well. Based on this result, a 5^th order feed forward has been designed. When a curve which can derivate by five times is inputted, the experimental results show that the maximum trajectory has been minimized by 20μm.