Feedforward control of a piezoelectric flexure stage for AFM

We review basic issues in the control of scanning probe microscopes. To improve the performance of the present generation of instruments, we have developed a simple feedforward technique that nonetheless increases the effective bandwidth of the positioning stage by a factor of 15 over its standard operation. If the desired control signal is known in advance (as it is for a periodic scan signal), the feedforward filter can be non-causal: information about the future can be used to cancel the phase lag produced by the stage response. We compare our design with other control techniques. We show that model-based iterative control algorithms can lead to a substantial performance boost, at the cost of more measurements of the system transfer function. We then introduce a model-free variant that is simpler to set up, performs better, and is more robust to system changes.