Bandwidth Based Repetitive Controller Design for a Modular Multi-actuated AFM Scanner

Abstract

High-Speed Atomic Force Micrscopy (HSAFM) enables visualization of dynamic processes and helps with understanding of fundamental behaviors at the nano-scale. Ideally, the HSAFM video frames should have high fidelity, high resolution, and a wide scanning range. Unfortunately, it is very difficult for scanners to simultaneously achieve high scanning bandwidth and large range. Since the first bending mode of large piezos is a major limiting factor, we propose an alternative design by stacking multiple short range piezo actuators. This approach allows significant increase of scanner bandwidth (over 20 kHz) while maintaining large travel range (over 20 μm). The modular design also facilitates the easy adjustment of scanner travel range. In this paper, we first discuss the design and assembly of this scanner. We then present the modeling and control of this multi-actuated scanner. A comparative study is then given on the performance of different controllers. These include a PID controller, a LQR based controller and a bandwidth based repetitive controller. The proposed algorithm provides significant improvement in tracking performance when utilized with the scanner using optimized input trajectories.