Fuzzy sliding mode control of piezo-driven stage

The motion stage with flexible hinges as a guiding mechanism can realize nanometer-level precision positioning. This stage uses a piezoelectric (PZT) actuator as the driving unit. In order to describe the mechanical characteristics of this piezo-driven stage, a double-parallel four-bar mechanism based on eight flexible hinges is analyzed. The natural frequency and modal of this stage are analyzed with the finite element method. In order to reduce the hysteresis influence of the PZT actuator, the model parameters based on the Bouc-Wen hysteresis model are identified by using the particle swarm optimization algorithm, and the boundedness of the hysteresis phenomenon is determined by this model. On this basis, the PZT hysteresis is regarded as a disturbance, and a proportional-integral-differential (PID)-type fuzzy sliding mode control (FSMC) is designed. Taking errors and the derivation in the errors as input and the parameters of the PID sliding surface as the output, the fuzzy sliding mode function is constructed. In addition, taking the absolute value of the sliding mode function as the input and the adjustment factor of the switching control as the output, the fuzzy switching control is constructed. Finally, the effectiveness of the FSMC is verified through several experiments.