Design and Control of a Multi-actuated High-bandwidth and Large-range Scanner for Atomic Force Microscopy

Atomic force microscopes (AFMs) with high-speed and large-range capabilities open up possibilities for many new applications. It is desirable to have a large scanning range along with zooming ability to obtain high resolution and high frame-rate imaging. Such capabilities will increase the imaging throughput and allow more sophisticated observations at the nanoscale. Unfortunately, in-plane scanning of conventional piezo tube scanners typically covers a large range of hundreds of microns but has limited bandwidth up to several hundred Hertz. The main focus of this paper is the multi-actuated piezo scanner design and control algorithm to achieve high-speed tracking. Three design strategies for structure bandwidth and operational range consideration are presented and evaluated. The non-linear hysteresis effect of the piezo actuators is modeled using the Preisach hysteresis model. PID control, iterative learning control and repetitive control strategies were investigated in simulation. Based on the controllers performance, the repetitive controller is implemented on a high-speed FPGA device and experimentally verified. The new AFM scanner design is capable of 10 kHz tracking at 3 μm range and 200 Hz tracking at 100 μm range.