Modeling and compound control of bellows-driven ultra-precision positioning stage

In order to improve the stroke and precision of the ultra-precision positioning stage, a new type of pneumatic servo positioning stage was designed. Air bearing sliders were designed by finite element method and metal bellows were used as the single driving device in the positioning stage. The stage was supported by aerostatic sliders to realize large stoke and ultra-precision positioning. The mechanical characteristics of bellows were analyzed with the experimental data. According to the initial loading curve, the parameters were identified to establish the PI hysteresis model of the system, and the model was validated by the experiments. In order to improve dynamic performance of the system, a compound control scheme was designed. In this scheme, a feedforward controller was based on inverse PI model, and a PID controller was used as feedback controller, the parameters of the PID controller were optimized by particle swarm optimization. Experiments on the step signal, sawtooth signal and sine signal were implemented. After the parameters are optimized, the experimental results show that the positioning accuracy on the step response is less than 50nm, the average tracking error on sawtooth input signal is 0.12 μm, and the average tracing error on sine input signal is 0.18 μm, the stage can meet the requirements of ultra-precision positioning.