A Nano Positioning Platform for STM and Its Compound Control Algorithm

Nano positioning platform, which is widely used in micro and nano measurement field such as scanning tunneling microscope (STM), becomes an indispensable multi-dimensional driving actuator. A good positioning platform is composed of precise mechanical structure, hardware circuits of signal detection, and software control algorithms. However, the nonlinear hysteresis characteristics of piezoelectric actuator (PZT), a common driver, affect the positioning accuracy. Therefore, it is significant to solve the nonlinearity for precise tracking. A nano positioning platform for STM is set up in this article. We propose a compound control algorithm of Bouc–Wen model and fuzzy–proportional–integral–derivative (PID) for STM to compensate and handle PZT's hysteresis. First, the Bouc–Wen model is established, whose parameters are identified by the genetic algorithm (GA), and the inverse discrete model data can be calculated. Then, the fuzzy theory is applied to the parameters' self-tuning of the traditional PID algorithm. Finally, the compound control combines open loop and closed loop, which achieves fast response, low overshoot, high precision, and favorable stability. The experimental results show that the proposed algorithm suitable for self-made STM nano positioning platform with small volume, open structure, convenient secondary transformation, easy disassembly, and self-tuning function can greatly improve the hysteresis nonlinearity and realize the accurate positioning.